document and make explicit desired noinline property for __init_libc
on multiple occasions I've started to flatten/inline the code in
__init_libc, only to rediscover the reason it was not inlined: GCC
fails to deallocate its stack (and now, with the changes in commit
4390383b32250a941ec616e8bff6f568a801b1c0, fails to produce a tail call
to the stage 2 function; see PR #87639) before calling main if it was
inlined.
document this with a comment and use an explicit noinline attribute if
__GNUC__ is defined so that even with CFLAGS that heavily favor
inlining it won't get inlined.
diff --git a/src/env/__libc_start_main.c b/src/env/__libc_start_main.c
index ba4d213..2e5f9dc 100644
--- a/src/env/__libc_start_main.c
+++ b/src/env/__libc_start_main.c
@@ -17,6 +17,9 @@
#define AUX_CNT 38
+#ifdef __GNUC__
+__attribute__((__noinline__))
+#endif
void __init_libc(char **envp, char *pn)
{
size_t i, *auxv, aux[AUX_CNT] = { 0 };
@@ -69,6 +72,9 @@
{
char **envp = argv+argc+1;
+ /* External linkage, and explicit noinline attribute if available,
+ * are used to prevent the stack frame used during init from
+ * persisting for the entire process lifetime. */
__init_libc(envp, argv[0]);
/* Barrier against hoisting application code or anything using ssp
