rhel:Correct the usage of __attribute__

[zhangzikang01]

Signed-off-by: zhangzikang01 zhangzikang@kylinos.cn

Comparison of the librelp-1.2.16 version reveals that the librelp.so.0 library generated by compiling the current version of the source code no longer includes the relpEngineGetVersion symbol, which does not meet compatibility requirements. Therefore, an analysis of the source code was conducted.

The analysis found that in the Makefile.am file, "AM_CFLAGS=-fvisibility=hidden" was added, setting the default attribute to hidden. Then, during function definition, the attribute was modified to default via "attribute((visibility("default")))". However, modifying the attribute to default at the definition location of the relpEngineGetVersion function did not take effect. The relpEngineGetVersion function retained the hidden attribute, resulting in the absence of the relpEngineGetVersion symbol in the compiled librelp.so.0 library.

Consult the information in the following link:
https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html

The material indicates that for functions, the attribute should be placed either before the declaration type or at the very end of the function.

A test demo was written to verify the usage of attribute:

#include <stdio.h>

#define PART_OF_API attribute((visibility("default")))
#define VERSION "1.11.0"
#define CH 't'

const char * test_0(void)
{
return (char*) (VERSION);
}

const char * PART_OF_API test_1(void)
{
return (char*) (VERSION);
}

PART_OF_API const char * test_2(void)
{
return (char*) (VERSION);
}

void main()
{
printf("test!\n");
}

gcc -fvisibility=hidden test.c -o libtest.o

test.c:13:1: warning: the 'visibility' attribute is ignored on a non-class type [-Wattributes]
13 | {
| ^

readelf -sW libtest.o | grep test_

70: 0000000000400690    12 FUNC    GLOBAL HIDDEN    13 test_1
81: 000000000040069c    12 FUNC    GLOBAL DEFAULT   13 test_2
86: 0000000000400684    12 FUNC    GLOBAL HIDDEN    13 test_0

---

Based on the test results, it was found that:

(1) Without adding attribute((visibility("default"))): the attribute remains hidden.
(2) Adding attribute((visibility("default"))) before the declaration type: the attribute is successfully modified to default.
(3) Adding attribute((visibility("default"))) between the declaration type and the function name: the attribute modification does not take effect, remains hidden, and a warning is generated (though warning messages are suppressed in the source code: #pragma GCC diagnostic ignored "-Wattributes").

Therefore, it is preliminarily determined that the incorrect placement of attribute((visibility("default"))) caused the attribute modification to fail. Hence, this PR is submitted to address the issue.

[gemini-code-assist]

Summary of Changes

Hello @zhangzikang01, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical compatibility issue in the librelp library where several API functions, notably relpEngineGetVersion, were unintentionally hidden due to incorrect placement of GCC's __attribute__((visibility("default"))) directive. The changes involve systematically repositioning this attribute to ensure proper symbol export, thereby restoring expected library functionality and preventing future regressions related to symbol visibility.

Highlights

• Symbol Visibility Fix: Corrected the placement of the __attribute__((visibility("default"))) directive for numerous API functions across src/relp.c, src/relpclt.c, and src/relpsrv.c to ensure they are properly exported in the librelp.so.0 shared library.
• Compatibility Restoration: This change specifically addresses a regression where the relpEngineGetVersion symbol was missing from the compiled library, thereby restoring compatibility with previous versions that expected this symbol to be available.
• Standardized Attribute Placement: The PART_OF_API macro, which defines the visibility attribute, has been consistently moved from after the function's return type to before it, aligning with GCC's recommended usage for function attributes.
• Removed Warning Suppression: The #pragma GCC diagnostic ignored "-Wattributes" directive, which was suppressing warnings about incorrect attribute usage for relpEngineGetVersion, has been removed, allowing the compiler to correctly flag such issues in the future.

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[gemini-code-assist]

Code Review

This pull request correctly addresses an issue with GCC attribute usage for symbol visibility. The analysis in the description is thorough and the fix is applied consistently across the codebase. By moving the PART_OF_API macro before the return type in function definitions, you've ensured that the functions are correctly exported in the shared library, which is crucial for compatibility. The removal of the pragma to suppress attribute warnings is also a good cleanup, as the root cause of the warning is now fixed. I've added one minor style suggestion for consistency.