[BUG] gettid() optimization

[vvb2060]

Description

#include <stdio.h>
#include <unistd.h>
#include <syscall.h>
#include <sys/wait.h>

int main(int argc, char *argv[]) {
    printf("p getpid()=%d gettid()=%d\n", getpid(), gettid());
    int pid = fork();
    if (pid == 0) {
        printf("getpid()=%d gettid()=%d NR_getpid=%ld NR_gettid=%ld\n", getpid(), gettid(),
               syscall(__NR_getpid), syscall(__NR_gettid));
    } else if (pid > 0) {
        waitpid(pid, nullptr, 0);
    }
    return 0;
}

release build and exec

p getpid()=22023 gettid()=22023
getpid()=22024 gettid()=22023 NR_getpid=22024 NR_gettid=22024

decompile

__int64 sub_888()
{
  unsigned int v0; // w20
  unsigned int v1; // w19
  int v2; // w0
  unsigned int v3; // w20
  __int64 v4; // x21
  __int64 v5; // x0

  v0 = getpid();
  v1 = gettid();
  printf("p getpid()=%d gettid()=%d\n", v0, v1);
  v2 = fork();
  if ( v2 )
  {
    if ( v2 >= 1 )
      waitpid(v2, 0LL, 0);
  }
  else
  {
    v3 = getpid();
    v4 = syscall(172LL);
    v5 = syscall(178LL);
    printf("getpid()=%d gettid()=%d NR_getpid=%ld NR_gettid=%ld\n", v3, v1, v4, v5);
  }
  return 0LL;
}

Affected versions

r27

Canary version

No response

Host OS

Windows

Host OS version

Windows10

Affected ABIs

arm64-v8a

Build system

ndk-build

Other build system

No response

minSdkVersion

23

Device API level

34

[enh-google]

yeah, the __attribute__((__const__)) on gettid() is unsafe in any function that calls fork() or equivalent. fixed by https://android-review.googlesource.com/c/platform/bionic/+/3106497.

[DanAlbert]

Since I still need to pull an updated toolchain for r27 RC 1, I'll do another sysroot update to grab this as well.