Re: [PATCH 1/3] powerpc/vmlinux.lds: Define RUNTIME_DISCARD_EXIT

[Michael Ellerman]

On Fri, 6 Jan 2023 00:23:47 +1100, Michael Ellerman wrote:
> The powerpc linker script explicitly includes .exit.text, because
> otherwise the link fails due to references from __bug_table and
> __ex_table. The code is freed (discarded) at runtime along with
> .init.text and data.
> 
> That has worked in the past despite powerpc not defining
> RUNTIME_DISCARD_EXIT because DISCARDS appears late in the powerpc linker
> script (line 410), and the explicit inclusion of .exit.text
> earlier (line 280) supersedes the discard.
> 
> [...]

Applied to powerpc/fixes.

[1/3] powerpc/vmlinux.lds: Define RUNTIME_DISCARD_EXIT
  https://git.kernel.org/powerpc/c/4b9880dbf3bdba3a7c56445137c3d0e30aaa0a40
[2/3] powerpc/vmlinux.lds: Don't discard .rela* for relocatable builds
  https://git.kernel.org/powerpc/c/07b050f9290ee012a407a0f64151db902a1520f5
[3/3] powerpc/vmlinux.lds: Don't discard .comment
  https://git.kernel.org/powerpc/c/be5f95c8779e19779dd81927c8574fec5aaba36c

cheers

[PATCH 1/3] powerpc/vmlinux.lds: Define RUNTIME_DISCARD_EXIT

[Michael Ellerman]

The powerpc linker script explicitly includes .exit.text, because
otherwise the link fails due to references from __bug_table and
__ex_table. The code is freed (discarded) at runtime along with
.init.text and data.

That has worked in the past despite powerpc not defining
RUNTIME_DISCARD_EXIT because DISCARDS appears late in the powerpc linker
script (line 410), and the explicit inclusion of .exit.text
earlier (line 280) supersedes the discard.

However commit 99cb0d917ffa ("arch: fix broken BuildID for arm64 and
riscv") introduced an earlier use of DISCARD as part of the RO_DATA
macro (line 136). With binutils < 2.36 that causes the DISCARD
directives later in the script to be applied earlier [1], causing
.exit.text to actually be discarded at link time, leading to build
errors:

  '.exit.text' referenced in section '__bug_table' of crypto/algboss.o: defined 
in
  discarded section '.exit.text' of crypto/algboss.o
  '.exit.text' referenced in section '__ex_table' of drivers/nvdimm/core.o: 
defined in
  discarded section '.exit.text' of drivers/nvdimm/core.o

Fix it by defining RUNTIME_DISCARD_EXIT, which causes the generic
DISCARDS macro to not include .exit.text at all.

1: https://lore.kernel.org/lkml/87fscp2v7k@igel.home/

Fixes: 99cb0d917ffa ("arch: fix broken BuildID for arm64 and riscv")
Signed-off-by: Michael Ellerman 
---
 arch/powerpc/kernel/vmlinux.lds.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S 
b/arch/powerpc/kernel/vmlinux.lds.S
index 8c3862b4c259..c5ea7d03d539 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -8,6 +8,7 @@
 #define BSS_FIRST_SECTIONS *(.bss.prominit)
 #define EMITS_PT_NOTE
 #define RO_EXCEPTION_TABLE_ALIGN   0
+#define RUNTIME_DISCARD_EXIT
 
 #define SOFT_MASK_TABLE(align) \
. = ALIGN(align);   \
-- 
2.39.0