Monday, July 3, 2017

FltCreateFile and top device.

FltCreateFile calls IoCreateFileEx with IO_DRIVER_CREATE_CONTEXT.DeviceObjectHint pointing to the Filter Manager's filter object and then calls the lower registered filters. That allows the created file object to have TopDeviceObjectHint pointing to the Filter Manager's object.
 # Child-SP          RetAddr           Call Site
00 ffffe101`3fffebf8 fffff801`92125200 FLTMGR!FltpCreate
01 ffffe101`3fffec00 fffff801`9213058b nt!IopParseDevice+0x7f0
02 ffffe101`3fffedd0 fffff801`921340c0 nt!ObpLookupObjectName+0x46b
03 ffffe101`3fffefa0 fffff801`9213803a nt!ObOpenObjectByNameEx+0x1e0
04 ffffe101`3ffff0e0 fffff801`920b0eb4 nt!IopCreateFile+0x3aa
05 ffffe101`3ffff180 fffff808`485240d5 nt!IoCreateFileEx+0x124
06 ffffe101`3ffff210 fffff808`4853d32d FLTMGR!FltpCreateFile+0x1cd
07 ffffe101`3ffff310 fffff808`4b6a79f8 FLTMGR!FltCreateFile+0x8d
08 ffffe101`3ffff3a0 fffff808`484f4b4c avscan!AvPreCreate+0x378 [d:\work\avscan\filter\avscan.c @ 2106]
09 ffffe101`3ffff4b0 fffff808`484f46ec FLTMGR!FltpPerformPreCallbacks+0x2ec
0a ffffe101`3ffff5d0 fffff808`48526117 FLTMGR!FltpPassThroughInternal+0x8c
0b ffffe101`3ffff600 fffff801`92125200 FLTMGR!FltpCreate+0x2d7
0c ffffe101`3ffff6b0 fffff801`9213058b nt!IopParseDevice+0x7f0
0d ffffe101`3ffff880 fffff801`921340c0 nt!ObpLookupObjectName+0x46b
0e ffffe101`3ffffa50 fffff801`920c9e90 nt!ObOpenObjectByNameEx+0x1e0

0: kd> dt nt!_FILE_OBJECT ffff948c621a3330
   +0x000 Type             : 0n5
   +0x002 Size             : 0n216
   +0x008 DeviceObject     : 0xffff948c`60a3bc80 _DEVICE_OBJECT
   +0x010 Vpb              : 0xffff948c`60a556e0 _VPB
   +0x018 FsContext        : 0xffff948c`6111a740 Void
   +0x020 FsContext2       : 0xffff8483`76cf78f0 Void
   +0x028 SectionObjectPointer : (null) 
   +0x030 PrivateCacheMap  : (null) 
   +0x038 FinalStatus      : 0n0
   +0x040 RelatedFileObject : (null) 
   +0x048 LockOperation    : 0 ''
   +0x049 DeletePending    : 0 ''
   +0x04a ReadAccess       : 0x1 ''
   +0x04b WriteAccess      : 0 ''
   +0x04c DeleteAccess     : 0 ''
   +0x04d SharedRead       : 0x1 ''
   +0x04e SharedWrite      : 0x1 ''
   +0x04f SharedDelete     : 0x1 ''
   +0x050 Flags            : 0x40000
   +0x058 FileName         : _UNICODE_STRING "\"
   +0x068 CurrentByteOffset : _LARGE_INTEGER 0x0
   +0x070 Waiters          : 0
   +0x074 Busy             : 0
   +0x078 LastLock         : (null) 
   +0x080 Lock             : _KEVENT
   +0x098 Event            : _KEVENT
   +0x0b0 CompletionContext : (null) 
   +0x0b8 IrpListLock      : 0
   +0x0c0 IrpList          : _LIST_ENTRY [ 0xffff948c`621a33f0 - 0xffff948c`621a33f0 ]
   +0x0d0 FileObjectExtension : 0xffff948c`6226f1b0 Void
   
0: kd> dq 0xffff948c`6226f1b0
ffff948c`6226f1b0  00000000`00000000 00000000`00000000
ffff948c`6226f1c0  ffff948c`60dff0d0 00000000`00000000
ffff948c`6226f1d0  ffff948c`6243f2c0 00000000`00000000
ffff948c`6226f1e0  00000000`00000000 00000000`00000000
ffff948c`6226f1f0  00000000`00000000 00000000`00000000
ffff948c`6226f200  61436d4d`02120006 00000000`0000034c
ffff948c`6226f210  ffff8483`7535ed10 ffff948c`62161e28
ffff948c`6226f220  ffff948c`6221da78 00000000`00000000

0: kd> dq ffff948c`60dff0d0
ffff948c`60dff0d0  ffff948c`610734a0 00000000`00000000
ffff948c`60dff0e0  00000000`00000000 00000000`00000000
ffff948c`60dff0f0  65536d4d`02060003 6c8da38a`069a7123
ffff948c`60dff100  00000000`00000000 0000024e`49c8000a
ffff948c`60dff110  0000024e`49c80fff 00000000`00000000
ffff948c`60dff120  00000000`00000000 00000000`00000000
ffff948c`60dff130  00000000`00000000 00000000`00000000
ffff948c`60dff140  00000000`00000002 00000000`00000000

0: kd> !object ffff948c`610734a0
Object: ffff948c610734a0  Type: (ffff948c5e34eb00) Device
    ObjectHeader: ffff948c61073470 (new version)
    HandleCount: 0  PointerCount: 1
    
0: kd> !devstack ffff948c610734a0
  !DevObj           !DrvObj            !DevExt           ObjectName
> ffff948c610734a0  \FileSystem\FltMgr ffff948c610735f0  
  ffff948c61048060  \FileSystem\fastfatffff948c610481b0 
  
0: kd> !vpb 0xffff948c`60a556e0
Vpb at 0xffff948c60a556e0
Flags: 0x1 mounted 
DeviceObject: 0xffff948c61048060
RealDevice:   0xffff948c60a3bc80
RefCount: 8
Volume Label: 

Tuesday, June 27, 2017

Sunday, June 25, 2017

Magenta RISC-V booting

Below is an output of Magenta RISC-V port riscv-magenta

[1266874889.709] 00000.00000> Available physical memory: 2032dMB
[1266874889.709] 00000.00000> 
welcome to lk/MP

[1266874889.709] 00000.00000> INIT: cpu 0, calling hook 0xffffffff8006e2d4 (global_prng_seed) at level 0x30000, flags 0x1
[1266874889.709] 00000.00000> WARNING: System has insufficient randomness.  It is completely unsafe to use this system for any cryptographic applications.
[1266874889.709] 00000.00000> INIT: cpu 0, calling hook 0xffffffff800386b0 (elf_build_id) at level 0x3fffe, flags 0x1
[1266874889.709] 00000.00000> INIT: cpu 0, calling hook 0xffffffff800385f0 (version) at level 0x3ffff, flags 0x1
[1266874889.709] 00000.00000> version:
[1266874889.709] 00000.00000>  arch:     RISCV
[1266874889.709] 00000.00000>  platform: RISCV_RV64
[1266874889.709] 00000.00000>  target:   QEMU_RISCV_RV64
[1266874889.709] 00000.00000>  project:  MAGENTA_QEMU_RISCV_RV64
[1266874889.709] 00000.00000>  buildid:  GIT_0FBB50D3A8FC1D242E1D7A2921674579C9192D66_DIRTY_LOCAL
[1266874889.709] 00000.00000>  ELF build ID: be2909891fc4cce74084f5fa3f14d6e98903d3bb
[1266874889.709] 00000.00000> INIT: cpu 0, calling hook 0xffffffff80042f0c (vm_preheap) at level 0x3ffff, flags 0x1
[1266874889.709] 00000.00000> initializing heap
[1266874889.709] 00000.00000> INIT: cpu 0, calling hook 0xffffffff8004305c (vm) at level 0x50000, flags 0x1
[1266874889.709] 00000.00000> VM: reserving kernel region [ffffffff80000000, ffffffff800f7000) flags 0x28 name 'kernel_code'
[1266874889.709] 00000.00000> VM: reserving kernel region [ffffffff800f7000, ffffffff80139000) flags 0x8 name 'kernel_rodata'
[1266874889.709] 00000.00000> VM: reserving kernel region [ffffffff80139000, ffffffff8013c000) flags 0x18 name 'kernel_data'
[1266874889.709] 00000.00000> VM: reserving kernel region [ffffffff8013c000, ffffffff80166000) flags 0x18 name 'kernel_bss'
[1266874889.709] 00000.00000> VM: reserving kernel region [ffffffff8016a000, ffffffff8114b000) flags 0x18 name 'kernel_bootalloc'
[1266874889.709] 00000.00000> INIT: cpu 0, calling hook 0xffffffff8000197c (timer) at level 0x50003, flags 0x1
[00003.966] 00000.00000> initializing mp
[00003.966] 00000.00000> initializing threads
[00003.967] 00000.00000> initializing timers
[00003.967] 00000.00000> INIT: cpu 0, calling hook 0xffffffff800132d4 (debuglog) at level 0x6ffff, flags 0x1
[00003.970] 00000.00000> INIT: cpu 0, calling hook 0xffffffff8006e448 (global_prng_thread_safe) at level 0x6ffff, flags 0x1
[00003.971] 00000.00000> creating bootstrap completion thread
[00004.057] 00000.00000> top of bootstrap2()
[00004.058] 00000.00000> INIT: cpu 0, calling hook 0xffffffff80070c9c (dpc) at level 0x70000, flags 0x1
[00004.064] 00000.00000> INIT: cpu 0, calling hook 0xffffffff8009158c (magenta) at level 0x70000, flags 0x1
[00004.078] 00000.00000> initializing platform
[00004.078] 00000.00000> initializing target
[00004.078] 00000.00000> calling apps_init()
[00004.078] 00000.00000> INIT: cpu 0, calling hook 0xffffffff80014464 (ktrace) at level 0xaffff, flags 0x1
[00005.091] 00000.00000> ktrace: buffer at 0xffffffc000e01000 (33554432 bytes)
[00005.094] 00000.00000> INIT: cpu 0, calling hook 0xffffffff800384bc (userboot) at level 0xaffff, flags 0x1
[00005.161] 00000.00000> userboot: userboot rodata       0 @ [0x292f043000,0x292f045000)
[00005.163] 00000.00000> userboot: userboot code    0x2000 @ [0x292f045000,0x292f05a000)
[00005.165] 00000.00000> userboot: vdso/full rodata       0 @ [0x292f05a000,0x292f05f000)
[00005.167] 00000.00000> userboot: vdso/full code    0x5000 @ [0x292f05f000,0x292f061000)
[00005.193] 00000.00000> userboot: entry point             @ 0x292f046da0
[00005.293] 00000.00000> starting app shell
] [00005.296] 00000.00000> entering main console loop

Monday, June 19, 2017

RISC-V Magenta context switch


The code related to RISC-V Magenta context switching can be found in exception.S  and switch_to.h files.
A thread for a CPU is switched by a call to
static inline void riscv_switch_to(struct riscv_thread_state * prev,
                                   struct riscv_thread_state * next)
{
    __switch_to_aux(prev, next);
    __switch_to(prev, next);
    assert(get_current());
}
The registers are saved and restored from the riscv_thread_state structure.
/*
 * Integer register context switch
 * The callee-saved registers must be saved and restored.
 * 
 *   a0: previous task_struct (must be preserved across the switch)
 *   a1: next task_struct
 */
.section .text
FUNCTION(__switch_to)
    /*
    * $a0 == &prev->arch.stat
    * $a1 == &next->arch.stat
    */
    /* Save context into prev->arch.state */
    REG_S ra,  THREAD_RA(a0)
    REG_S sp,  THREAD_SP(a0)
    REG_S s0,  THREAD_S0(a0)
    REG_S s1,  THREAD_S1(a0)
    REG_S s2,  THREAD_S2(a0)
    REG_S s3,  THREAD_S3(a0)
    REG_S s4,  THREAD_S4(a0)
    REG_S s5,  THREAD_S5(a0)
    REG_S s6,  THREAD_S6(a0)
    REG_S s7,  THREAD_S7(a0)
    REG_S s8,  THREAD_S8(a0)
    REG_S s9,  THREAD_S9(a0)
    REG_S s10, THREAD_S10(a0)
    REG_S s11, THREAD_S11(a0)
    /* Restore context from next->arch.state */
    REG_L ra,  THREAD_RA(a1)
    REG_L sp,  THREAD_SP(a1)
    REG_L s0,  THREAD_S0(a1)
    REG_L s1,  THREAD_S1(a1)
    REG_L s2,  THREAD_S2(a1)
    REG_L s3,  THREAD_S3(a1)
    REG_L s4,  THREAD_S4(a1)
    REG_L s5,  THREAD_S5(a1)
    REG_L s6,  THREAD_S6(a1)
    REG_L s7,  THREAD_S7(a1)
    REG_L s8,  THREAD_S8(a1)
    REG_L s9,  THREAD_S9(a1)
    REG_L s10, THREAD_S10(a1)
    REG_L s11, THREAD_S11(a1)
    REG_L tp,  THREAD_TI(a1) /* Next thread_info pointer */
    /*return to $ra, the new $sp has been set*/
    ret
END(__switch_to)
The new thread $ra points to the next instruction after a call to __switch_to inside riscv_switch_to
(gdb) p/x newthread->arch.state
$137 = {ra = 0xffffffff80002f3c, sp = 0xffffffff8114cc80, s = {0xffffffff8114ccb0, 0xffffffff800031c4, 0x1, 0xffffffff800347f8, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0}, fstate = {f = {
      0x0 <repeats 32 times>}, fcsr = 0x0}, ti = 0xffffffff8114ae80}
The ret instruction at the end of __switch_to resumes a thread at this address.
The scheduled out thread state has $ra pointing to same address.
(gdb) p/x oldthread->arch.state
$138 = {ra = 0xffffffff8000b3f8, sp = 0xffffffc002e04000, s = {0x0 <repeats 12 times>}, fstate = {f = {0x0 <repeats 32 times>}, fcsr = 0x0}, ti = 0xffffffff8116a9d8}
The riscv_switch_to disassembled listing is
(gdb) disassem 0xffffffff80002f3c
Dump of assembler code for function riscv_switch_to:
   0xffffffff80002f04 <+0>: addi sp,sp,-48
   0xffffffff80002f08 <+4>: sd ra,40(sp)
   0xffffffff80002f0c <+8>: sd s0,32(sp)
   0xffffffff80002f10 <+12>: sd s1,24(sp)
   0xffffffff80002f14 <+16>: addi s0,sp,48
   0xffffffff80002f18 <+20>: mv s1,ra
   0xffffffff80002f1c <+24>: sd a0,-40(s0)
   0xffffffff80002f20 <+28>: sd a1,-48(s0)
   0xffffffff80002f24 <+32>: ld a1,-48(s0)
   0xffffffff80002f28 <+36>: ld a0,-40(s0)
   0xffffffff80002f2c <+40>: jal ra,0xffffffff80002ee0 <__switch_to_aux>
   0xffffffff80002f30 <+44>: ld a1,-48(s0)
   0xffffffff80002f34 <+48>: ld a0,-40(s0)
   0xffffffff80002f38 <+52>: jal ra,0xffffffff800003a8 <__switch_to>
   0xffffffff80002f3c <+56>: jal ra,0xffffffff80002e70 <get_current>
   0xffffffff80002f40 <+60>: mv a5,a0
   0xffffffff80002f44 <+64>: seqz a5,a5
   0xffffffff80002f48 <+68>: andi a5,a5,255
   0xffffffff80002f4c <+72>: beqz a5,0xffffffff80002f78 <riscv_switch_to+116>
   0xffffffff80002f50 <+76>: mv a0,s1
   0xffffffff80002f54 <+80>: mv a1,s0
   0xffffffff80002f58 <+84>: lui a5,0x800f2
   0xffffffff80002f5c <+88>: addi a5,a5,1880 # 0xffffffff800f2758
   0xffffffff80002f60 <+92>: li a4,34
   0xffffffff80002f64 <+96>: lui a3,0x800f2
   0xffffffff80002f68 <+100>: addi a3,a3,1896 # 0xffffffff800f2768
   0xffffffff80002f6c <+104>: lui a2,0x800f2
   0xffffffff80002f70 <+108>: addi a2,a2,1840 # 0xffffffff800f2730
   0xffffffff80002f74 <+112>: jal ra,0xffffffff8006b9f0 <_panic>
   0xffffffff80002f78 <+116>: nop
   0xffffffff80002f7c <+120>: ld ra,40(sp)
   0xffffffff80002f80 <+124>: ld s0,32(sp)
   0xffffffff80002f84 <+128>: ld s1,24(sp)
   0xffffffff80002f88 <+132>: addi sp,sp,48
   0xffffffff80002f8c <+136>: ret
As you can see 0xffffffff80002f3c is an address of a call to get_current which is a parameter to the assert check after a call to __switch_to.

Monday, June 12, 2017

RISC-V Magenta. The init process.

The init process address space initialisation.
#2  0xffffffff80004690 in arch_mmu_init_aspace (aspace=0xffffffff81168310, base=16777216, size=274861125632, flags=0) at kernel/arch/riscv/mmu.cpp:73
#3  0xffffffff8004bb64 in VmAspace::Init (this=0xffffffff811681c0) at kernel/kernel/vm/vm_aspace.cpp:142
#4  0xffffffff8004bdb0 in VmAspace::Create (flags=0, name=0x0) at kernel/kernel/vm/vm_aspace.cpp:180
#5  0xffffffff8008f7e0 in ProcessDispatcher::Initialize (this=0xffffffff81167eb0) at kernel/lib/magenta/process_dispatcher.cpp:147
#6  0xffffffff8008ef30 in ProcessDispatcher::Create (job=..., name=..., flags=0, dispatcher=0xffffffff81146e48, rights=0xffffffff81146e3c, root_vmar_disp=0xffffffff81146e40, 
    root_vmar_rights=0xffffffff81146e38) at kernel/lib/magenta/process_dispatcher.cpp:73
#7  0xffffffff80032b84 in attempt_userboot () at kernel/lib/userboot/userboot.cpp:283
#8  0xffffffff800330ec in userboot_init (level=720895) at kernel/lib/userboot/userboot.cpp:357
#9  0xffffffff80005da8 in lk_init_level (required_flag=LK_INIT_FLAG_PRIMARY_CPU, start_level=655360, stop_level=720895) at kernel/top/init.c:86
#10 0xffffffff80005e4c in lk_primary_cpu_init_level (start_level=655360, stop_level=720895) at kernel/include/lk/init.h:51
#11 0xffffffff800060fc in bootstrap2 (arg=0x0) at kernel/top/main.c:136
#12 0xffffffff8000a78c in initial_thread_func () at kernel/kernel/thread.c:84
#13 0xffffffff8000a74c in init_thread_struct (t=0xffffffff81144be0, name=0x0) at kernel/kernel/thread.c:72

Thursday, June 8, 2017

Windows. Cache prefetching


00 nt!KiSwapContext
01 nt!KiSwapThread
02 nt!KiCommitThreadWait
03 nt!KeWaitForSingleObject
04 nt!MiWaitForInPageComplete
05 nt!MiPfCompleteInPageSupport
06 nt!MiPfCompletePrefetchIos
07 nt!MmWaitForCacheManagerPrefetch
08 nt!CcFetchDataForRead
09 nt!CcMapAndCopyFromCache
0a nt!CcCopyReadEx
0b nt!CcCopyRead

Tuesday, May 30, 2017

RISC-V GNU tool chain and relocation sections in shared and static libraries.

The library code
const
unsigned char __clz_tab[] =
{
  0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
  6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
  8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
  8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
  8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
  8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,
};

long foo(long x)
{
    return __clz_tab[x % (sizeof(__clz_tab)/sizeof(__clz_tab[0]))];
}
Build the shared(.so) and static(.o) library.
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-gcc  -shared -ffreestanding -nostdlib -fPIC  -o relocation.so relocation.c
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-gcc  -c -ffreestanding -nostdlib -fPIC  -o relocation.o relocation.c
The shared library has a .got (Global Offset Table) section to reference the __clz_tab array. The .got section is adjusted by the loader with the relocation data from the .rela.dyn section.
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-objdump -hr relocation.so

relocation.so:     file format elf64-littleriscv

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .hash         00000030  00000000000000e8  00000000000000e8  000000e8  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  1 .dynsym       000000a8  0000000000000118  0000000000000118  00000118  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  2 .dynstr       00000027  00000000000001c0  00000000000001c0  000001c0  2**0
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  3 .rela.dyn     00000018  00000000000001e8  00000000000001e8  000001e8  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  4 .text         00000038  0000000000000200  0000000000000200  00000200  2**2
                  CONTENTS, ALLOC, LOAD, READONLY, CODE
  5 .rodata       00000100  0000000000000238  0000000000000238  00000238  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  6 .dynamic      000000e0  0000000000001338  0000000000001338  00000338  2**3
                  CONTENTS, ALLOC, LOAD, DATA
  7 .got          00000020  0000000000001418  0000000000001418  00000418  2**3
                  CONTENTS, ALLOC, LOAD, DATA
  8 .comment      00000011  0000000000000000  0000000000000000  00000438  2**0
                  CONTENTS, READONLY
                  
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-objdump --disassemble relocation.so

relocation.so:     file format elf64-littleriscv


Disassembly of section .text:

0000000000000200 <foo>:
 200: fe010113           addi sp,sp,-32
 204: 00813c23           sd s0,24(sp)
 208: 02010413           addi s0,sp,32
 20c: fea43423           sd a0,-24(s0)
 210: fe843783           ld a5,-24(s0)
 214: 0ff7f793           andi a5,a5,255
 218: 00001717           auipc a4,0x1
 21c: 21873703           ld a4,536(a4) # 1430 <_GLOBAL_OFFSET_TABLE_+0x8>
 220: 00f707b3           add a5,a4,a5
 224: 0007c783           lbu a5,0(a5)
 228: 00078513           mv a0,a5
 22c: 01813403           ld s0,24(sp)
 230: 02010113           addi sp,sp,32
 234: 00008067           ret
 
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-readelf -r  relocation.so

Relocation section '.rela.dyn' at offset 0x1e8 contains 1 entries:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000001430  000300000002 R_RISCV_64        0000000000000238 __clz_tab + 0
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-objdump -hr relocation.o

relocation.o:     file format elf64-littleriscv

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .text         00000038  0000000000000000  0000000000000000  00000040  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .data         00000000  0000000000000000  0000000000000000  00000078  2**0
                  CONTENTS, ALLOC, LOAD, DATA
  2 .bss          00000000  0000000000000000  0000000000000000  00000078  2**0
                  ALLOC
  3 .rodata       00000100  0000000000000000  0000000000000000  00000078  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  4 .comment      00000012  0000000000000000  0000000000000000  00000178  2**0
                  CONTENTS, READONLY
RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE 
0000000000000018 R_RISCV_GOT_HI20  __clz_tab
000000000000001c R_RISCV_PCREL_LO12_I  .L0 
The static library also has a .got (Global Offset Table) section to reference the __clz_tab array. The .got section is adjusted by the loader with the relocation data from the .rela.dyn section.
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-objdump -hr relocation.o

relocation.o:     file format elf64-littleriscv

Sections:
Idx Name          Size      VMA               LMA               File off  Algn
  0 .text         00000038  0000000000000000  0000000000000000  00000040  2**2
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
  1 .data         00000000  0000000000000000  0000000000000000  00000078  2**0
                  CONTENTS, ALLOC, LOAD, DATA
  2 .bss          00000000  0000000000000000  0000000000000000  00000078  2**0
                  ALLOC
  3 .rodata       00000100  0000000000000000  0000000000000000  00000078  2**3
                  CONTENTS, ALLOC, LOAD, READONLY, DATA
  4 .comment      00000012  0000000000000000  0000000000000000  00000178  2**0
                  CONTENTS, READONLY
RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE 
0000000000000018 R_RISCV_GOT_HI20  __clz_tab
000000000000001c R_RISCV_PCREL_LO12_I  .L0 

slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-objdump --disassemble relocation.o

relocation.o:     file format elf64-littleriscv


Disassembly of section .text:

0000000000000000 <foo>:
   0: fe010113           addi sp,sp,-32
   4: 00813c23           sd s0,24(sp)
   8: 02010413           addi s0,sp,32
   c: fea43423           sd a0,-24(s0)
  10: fe843783           ld a5,-24(s0)
  14: 0ff7f793           andi a5,a5,255

0000000000000018 <.L0 >:
  18: 00000717           auipc a4,0x0
  1c: 00073703           ld a4,0(a4) # 18 <.L0 >
  20: 00f707b3           add a5,a4,a5
  24: 0007c783           lbu a5,0(a5)
  28: 00078513           mv a0,a5
  2c: 01813403           ld s0,24(sp)
  30: 02010113           addi sp,sp,32
  34: 00008067           ret
  
slava@slava-P34V2:/work/risc-v/musl-riscv/tmp$ riscv64-unknown-linux-gnu-readelf -r  relocation.o

Relocation section '.rela.text' at offset 0x2a8 contains 2 entries:
  Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000018  000800000014 R_RISCV_GOT_HI20  0000000000000000 __clz_tab + 0
00000000001c  000600000018 R_RISCV_PCREL_LO1 0000000000000018 .L0  + 0