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boundary="===============0456853090352659194==" Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" --===============0456853090352659194== Content-Type: multipart/alternative; boundary="------------4B8A72D366D81FBC35BCBCBC" Content-Language: en-US --------------4B8A72D366D81FBC35BCBCBC Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit On 9/30/21 9:14 PM, Mathieu Desnoyers wrote: > > **[Please note: This e-mail is from an EXTERNAL e-mail address] > > ----- On Sep 29, 2021, at 11:47 PM, lttng-dev > wrote: > > 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. > > > I suspect it depends on which optimizations are being enabled at -Og > on each architecture. > The "_uatomic_link_error()" trick indeed depends on the compiler > optimizing away > unreachable calls. > > If you really intend on using "-Og" on arm32, trying building with > "-DUATOMIC_NO_LINK_ERROR". > It should take care of making sure to generate an illegal instruction > rather than rely on the linker > error. > > Thanks, > > Mathieu Thanks.  I have tried with "-DUATOMIC_NO_LINK_ERROR".  With this,  it can compile successfully. Changqing > > Thanks > > //Changqing > > > _______________________________________________ > lttng-dev mailing list > lttng-dev@lists.lttng.org > https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev > > > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com > --------------4B8A72D366D81FBC35BCBCBC Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit


On 9/30/21 9:14 PM, Mathieu Desnoyers wrote:

[Please note: This e-mail is from an EXTERNAL e-mail address]

----- On Sep 29, 2021, at 11:47 PM, lttng-dev <lttng-dev@lists.lttng.org> wrote:

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.


I suspect it depends on which optimizations are being enabled at -Og on each architecture.
The "_uatomic_link_error()" trick indeed depends on the compiler optimizing away
unreachable calls.

If you really intend on using "-Og" on arm32, trying building with "-DUATOMIC_NO_LINK_ERROR".
It should take care of making sure to generate an illegal instruction rather than rely on the linker
error.

Thanks,

Mathieu

Thanks.  I have tried with "-DUATOMIC_NO_LINK_ERROR".  With this,  it can compile successfully.

Changqing


Thanks

//Changqing


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--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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