[lttng-dev] with -Og option, lttng-ust compile failed on 32bit arm

[Changqing Li]

Hi,

The problem happened after upgrade to lttng-ust 2.13.0.  2.12.0 don't 
have this issue.

liburcu version: 0.13.0

gcc: 11.2.0

This is my reproduce steps, it is cross compile enviroment based on 
yocto project.

 1. git clone git://git.yoctoproject.org/poky
 2. . oe-init-build-env
 3. echo "MACHINE='qemuarm'" >> conf/local.conf
 4. echo "DEBUG_BUILD='1'" >> conf/local.conf
 5. bitbake lttng-ust

compile failed with error:

| 
/work/cortexa15t2hf-neon-poky-linux-gnueabi/lttng-ust/2_2.13.0-r0/recipe-sysroot-native/usr/bin/arm-poky-linux-gnueabi/../../libexec/arm-poky-linux-gnueabi/gcc/arm-poky-linux-gnueabi/11.2.0/ld: 
../../../src/lib/lttng-ust/.libs/liblttng-ust.so: undefined reference to 
`_uatomic_link_error'
| collect2: error: ld returned 1 exit status
| Makefile:399: recipe for target 'test_ust_error' failed

checked with "nm ../../../src/lib/lttng-ust/.libs/liblttng-ust.so" | 
grep atomic, we can see 'U _uatomic_link_error',  but since -Og

is used,  liburcu don't define this function.

[snip]
#if !defined __OPTIMIZE__  || defined UATOMIC_NO_LINK_ERROR
static inline __attribute__((always_inline, noreturn))
void _uatomic_link_error(void)
{
#ifdef ILLEGAL_INSTR
         /*
          * generate an illegal instruction. Cannot catch this with
          * linker tricks when optimizations are disabled.
          */
         __asm__ __volatile__(ILLEGAL_INSTR);
#else
         __builtin_trap();
#endif
}
#else /* #if !defined __OPTIMIZE__  || defined UATOMIC_NO_LINK_ERROR */
extern void _uatomic_link_error(void);
#endif /* #else #if !defined __OPTIMIZE__  || defined 
UATOMIC_NO_LINK_ERROR */

[snip]

we cannot see 'U _uatomic_link_error' in following conditions, so 
compile successed:

1.  without -Og(using -O2),  + 32bit arm

2. -Og + 64bit arm

3. -Og + x86/x86-64


Do you have any idea about how to fix this? I don't understand why only 
"-Og + 32bit arm" will call function _uatomic_link_error.

Thanks

//Changqing

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