linux-kernel - [PATCH/RFC] powerpc/module_64: allow .init

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Message-Id: <920acea9aa18e4f2956581a8e158bdaa376fdf63.1629203945.git.jstancek@redhat.com>
Date:   Tue, 17 Aug 2021 15:02:54 +0200
From:   Jan Stancek <jstancek@...hat.com>
To:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        christophe.leroy@...roup.eu, linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, jstancek@...hat.com
Subject: [PATCH/RFC] powerpc/module_64: allow .init_array constructors to run

gcov and kasan rely on compiler generated constructor code.
For modules, gcc-8 with gcov enabled generates .init_array section,
but on ppc64le it doesn't get executed. find_module_sections() never
finds .init_array section, because module_frob_arch_sections() renames
it to _init_array.

Avoid renaming .init_array section, so do_mod_ctors() can use it.

Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>
Signed-off-by: Jan Stancek <jstancek@...hat.com>
---
I wasn't able to trace the comment:
  "We don't handle .init for the moment: rename to _init"
to original patch (it pre-dates .git). I'm not sure if it
still applies today, so I limited patch to .init_array. This
fixes gcov for modules for me on ppc64le 5.14.0-rc6.

Renaming issue is also mentioned in kasan patches here:
  https://patchwork.ozlabs.org/project/linuxppc-dev/cover/20210319144058.772525-1-dja@axtens

 arch/powerpc/kernel/module_64.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 6baa676e7cb6..c604b13ea6bf 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -299,8 +299,16 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
 					  sechdrs[i].sh_size);
 
 		/* We don't handle .init for the moment: rename to _init */
-		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init")))
+		while ((p = strstr(secstrings + sechdrs[i].sh_name, ".init"))) {
+#ifdef CONFIG_CONSTRUCTORS
+			/* find_module_sections() needs .init_array intact */
+			if (strstr(secstrings + sechdrs[i].sh_name,
+				".init_array")) {
+				break;
+			}
+#endif
 			p[0] = '_';
+		}
 
 		if (sechdrs[i].sh_type == SHT_SYMTAB)
 			dedotify((void *)hdr + sechdrs[i].sh_offset,
-- 
2.27.0