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[libc] Refactor internal auxv usage to reduce getauxval dependencies #162489

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Merged
merged 2 commits into from
Oct 8, 2025
Merged

[libc] Refactor internal auxv usage to reduce getauxval dependencies #162489

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5b12e39
[libc] cleanup entrypoint dependency on getauxval
SchrodingerZhu Oct 8, 2025
70ec742
[libc] remove errno logic entirely from vDSO
SchrodingerZhu Oct 8, 2025
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3 changes: 1 addition & 2 deletions libc/src/__support/OSUtil/linux/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -70,11 +70,10 @@ add_object_library(
libc.src.__support.CPP.string_view
libc.src.__support.threads.callonce
libc.src.__support.threads.linux.futex_word_type
libc.src.__support.OSUtil.linux.auxv
libc.hdr.types.struct_timeval
libc.hdr.types.struct_timespec
libc.hdr.types.clockid_t
libc.hdr.types.time_t
libc.hdr.link_macros
libc.src.errno.errno
libc.src.sys.auxv.getauxval
)
13 changes: 4 additions & 9 deletions libc/src/__support/OSUtil/linux/vdso.cpp
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Expand Up @@ -11,10 +11,9 @@
#include "src/__support/CPP/array.h"
#include "src/__support/CPP/optional.h"
#include "src/__support/CPP/string_view.h"
#include "src/__support/libc_errno.h"
#include "src/__support/OSUtil/linux/auxv.h"
#include "src/__support/threads/callonce.h"
#include "src/__support/threads/linux/futex_word.h"
#include "src/sys/auxv/getauxval.h"
#include <linux/auxvec.h>

// TODO: This is a temporary workaround to avoid including elf.h
Expand Down Expand Up @@ -189,17 +188,13 @@ void Symbol::initialize_vdso_global_cache() {
for (auto &i : global_cache)
i = nullptr;

// get the address of the VDSO, protect errno since getauxval may change
// it
int errno_backup = libc_errno;
uintptr_t vdso_ehdr_addr = getauxval(AT_SYSINFO_EHDR);
cpp::optional<unsigned long> auxv_res = auxv::get(AT_SYSINFO_EHDR);
uintptr_t vdso_ehdr_addr = auxv_res ? static_cast<uintptr_t>(*auxv_res) : 0;
// Get the memory address of the vDSO ELF header.
auto vdso_ehdr = reinterpret_cast<ElfW(Ehdr) *>(vdso_ehdr_addr);
// leave the table unpopulated if we don't have vDSO
if (vdso_ehdr == nullptr) {
libc_errno = errno_backup;
if (vdso_ehdr == nullptr)
return;
}

// locate the section header inside the elf using the section header
// offset
Expand Down
4 changes: 2 additions & 2 deletions libc/src/unistd/linux/CMakeLists.txt
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Expand Up @@ -563,8 +563,8 @@ add_entrypoint_object(
DEPENDS
libc.include.unistd
libc.include.sys_auxv
libc.src.errno.errno
libc.src.sys.auxv.getauxval
libc.src.__support.libc_errno
libc.src.__support.OSUtil.linux.auxv
)

add_entrypoint_object(
Expand Down
11 changes: 7 additions & 4 deletions libc/src/unistd/linux/sysconf.cpp
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Expand Up @@ -11,17 +11,20 @@
#include "src/__support/common.h"

#include "hdr/unistd_macros.h"
#include "src/__support/OSUtil/linux/auxv.h"
#include "src/__support/libc_errno.h"
#include "src/__support/macros/config.h"
#include "src/sys/auxv/getauxval.h"
#include <sys/auxv.h>

namespace LIBC_NAMESPACE_DECL {

LLVM_LIBC_FUNCTION(long, sysconf, (int name)) {
long ret = 0;
if (name == _SC_PAGESIZE)
return static_cast<long>(getauxval(AT_PAGESZ));
if (name == _SC_PAGESIZE) {
cpp::optional<unsigned long> page_size = auxv::get(AT_PAGESZ);
if (page_size)
return static_cast<long>(*page_size);
ret = -1;
}

// TODO: Complete the rest of the sysconf options.
if (ret < 0) {
Expand Down
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