When the -ffunction-sections compiler option is enabled, each function
is placed in a separate section named .text.function_name rather than
putting all functions in a single .text section.
However, using -function-sections can cause problems with the
linker script. The comments included in include/asm-generic/vmlinux.lds.h
note these issues.:
“TEXT_MAIN here will match .text.fixup and .text.unlikely if dead
code elimination is enabled, so these sections should be converted
to use ".." first.”
It is unclear whether there is a straightforward method for converting
a suffix to "..". This patch modifies the order of subsections within the
text output section when the -ffunction-sections flag is enabled.
Specifically, it repositions sections with certain fixed patterns (for
example .text.unlikely) before TEXT_MAIN, ensuring that they are grouped
and matched together.
Note that the limitation arises because the linker script employs glob
patterns instead of regular expressions for string matching. While there
is a method to maintain the current order using complex patterns, this
significantly complicates the pattern and increases the likelihood of
errors.
Co-developed-by: Han Shen <shen...@google.com>
Signed-off-by: Han Shen <shen...@google.com>
Signed-off-by: Rong Xu <x...@google.com>
Suggested-by: Sriraman Tallam <tmsri...@google.com>
Suggested-by: Krzysztof Pszeniczny <kpszenic...@google.com>
---
include/asm-generic/vmlinux.lds.h | 17 +++++++++++++++--
1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h
b/include/asm-generic/vmlinux.lds.h
index eeadbaeccf88..5df589c60401 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -554,9 +554,21 @@
* during second ld run in second ld pass when generating System.map
*
* TEXT_MAIN here will match .text.fixup and .text.unlikely if dead
- * code elimination is enabled, so these sections should be converted
- * to use ".." first.
+ * code elimination or function-section is enabled. Match these symbols
+ * first when in these builds.
*/
+#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG)
+#define TEXT_TEXT \
+ ALIGN_FUNCTION(); \
+ *(.text.asan.* .text.tsan.*) \
+ *(.text.unknown .text.unknown.*) \
+ *(.text.unlikely .text.unlikely.*) \
+ . = ALIGN(PAGE_SIZE); \
+ *(.text.hot .text.hot.*) \
+ *(TEXT_MAIN .text.fixup) \
+ NOINSTR_TEXT \
+ *(.ref.text)
+#else
#define TEXT_TEXT \
ALIGN_FUNCTION(); \
*(.text.hot .text.hot.*) \
@@ -566,6 +578,7 @@
NOINSTR_TEXT \
*(.ref.text) \
*(.text.asan.* .text.tsan.*)
+#endif
/* sched.text is aling to function alignment to secure we have same
--
2.46.1.824.gd892dcdcdd-goog
