Re: [PATCH] powerpc32/modules: Reserve a PLT entry for ftrace_regs_caller

[Christophe Leroy (CS GROUP)]

Le 23/09/2026 à 19:56, Bradley Morgan a écrit :
Commit 7dfbfb87c243 ("powerpc/ftrace: Activate
HAVE_DYNAMIC_FTRACE_WITH_REGS on PPC32") made count_relocs()
undercount the PLT entries the loader
consumes: module_finalize_ftrace() now creates two trampolines
(mod->arch.tramp for ftrace_caller() and mod->arch.tramp_regs for
ftrace_regs_caller()), while count_relocs() reserves only one entry
for ftrace.

So the core .plt ends up one ppc_plt_entry (16 bytes) short. The
walk in do_plt_call() scans for a free slot with
"while (entry->jump[0])" and has no bound check, so once the last
reserved slot is used up, the walk steps past the end of the section
and patch_instruction() writes the 4-instruction trampoline into
whatever module memory follows the .plt.

Count the second entry, mirroring what module_64.c does for the same
pair of stubs.

Signed-off-by: Bradley Morgan <br...@mainlining.org>

I would have had a preference for something similar to commit 
c12cfe9dee07 ("powerpc/module_64: Convert #ifdef to IS_ENABLED()")

Nevertheless,

Reviewed-by: Christophe Leroy (CS GROUP) <chle...@kernel.org>



---
  arch/powerpc/kernel/module_32.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/kernel/module_32.c b/arch/powerpc/kernel/module_32.c
index f930e3395a7f..61152deffc55 100644
--- a/arch/powerpc/kernel/module_32.c
+++ b/arch/powerpc/kernel/module_32.c
@@ -41,6 +41,9 @@ static unsigned int count_relocs(const Elf32_Rela *rela, 
unsigned int num)
  
  #ifdef CONFIG_DYNAMIC_FTRACE
        _count_relocs++;        /* add one for ftrace_caller */
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+       _count_relocs++;        /* add one for ftrace_regs_caller */
+#endif
  #endif
        return _count_relocs;
  }