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[v2,06/15] tools/nolibc: compiler: use attribute((naked)) if available

Message ID 20240807-nolibc-llvm-v2-6-c20f2f5fc7c2@weissschuh.net (mailing list archive)
State Accepted
Commit e098eebb63cb1c03813559b5db9da4451ba3a318
Headers show
Series tools/nolibc: improve LLVM/clang support | expand

Commit Message

Thomas Weißschuh Aug. 7, 2024, 9:51 p.m. UTC 
The current entrypoint attributes optimize("Os", "omit-frame-pointer")
are intended to avoid all compiler generated code, like function
porologue and epilogue.
This is the exact usecase implemented by the attribute "naked".

Unfortunately this is not implemented by GCC for all targets,
so only use it where available.
This also provides compatibility with clang, which recognizes the
"naked" attribute but not the previously used attribute "optimized".

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
 tools/include/nolibc/compiler.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)
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Patch

diff --git a/tools/include/nolibc/compiler.h b/tools/include/nolibc/compiler.h
index 14a854929910..e4cb5cf772ee 100644
--- a/tools/include/nolibc/compiler.h
+++ b/tools/include/nolibc/compiler.h
@@ -12,8 +12,13 @@ 
 #  define __nolibc_has_attribute(attr) 0
 #endif
 
-#define __nolibc_naked __attribute__((optimize("Os", "omit-frame-pointer")))
-#define __nolibc_naked_epilogue() __builtin_unreachable()
+#if __nolibc_has_attribute(naked)
+#  define __nolibc_naked __attribute__((naked))
+#  define __nolibc_naked_epilogue()
+#else
+#  define __nolibc_naked __attribute__((optimize("Os", "omit-frame-pointer")))
+#  define __nolibc_naked_epilogue() __builtin_unreachable()
+#endif /* __nolibc_has_attribute(naked) */
 
 #if defined(__SSP__) || defined(__SSP_STRONG__) || defined(__SSP_ALL__) || defined(__SSP_EXPLICIT__)