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Subject[PATCH] x86/boot/compressed: Correct relocation destination on old linkers
Date
As described in commit 6d92bc9d483a ("x86/build: Build compressed x86
kernels as PIE"), pre-2.26 binutils generates R_386_32 relocations in
PIE mode. Since the startup code does not perform relocation, any reloc
entry with R_386_32 will remain as 0 in the executing code.

Commit 974f221c84b0 ("x86/boot: Move compressed kernel to the end of the
decompression buffer") added a new symbol _end but did not mark it
hidden, which doesn't give the correct offset on older linkers. This
doesn't cause a crash, but means the compressed kernel is actually
relocated starting from the end of the decompression buffer, rather than
ending there.

Mark _end as hidden to fix.

Fixes: 974f221c84b0 ("x86/boot: Move compressed kernel to the end of the decompression buffer")
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
arch/x86/boot/compressed/head_32.S | 5 +++--
arch/x86/boot/compressed/head_64.S | 1 +
2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index f2dfd6d083ef..e4d1142f9f65 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -49,16 +49,17 @@
* Position Independent Executable (PIE) so that linker won't optimize
* R_386_GOT32X relocation to its fixed symbol address. Older
* linkers generate R_386_32 relocations against locally defined symbols,
- * _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less
+ * _bss, _ebss, _got, _egot and _end, in PIE. It isn't wrong, just less
* optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle
* R_386_32 relocations when relocating the kernel. To generate
- * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as
+ * R_386_RELATIVE relocations, we mark _bss, _ebss, _got, _egot and _end as
* hidden:
*/
.hidden _bss
.hidden _ebss
.hidden _got
.hidden _egot
+ .hidden _end

__HEAD
SYM_FUNC_START(startup_32)
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 6eb30f8a3ce7..206fb95e827c 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -42,6 +42,7 @@
.hidden _ebss
.hidden _got
.hidden _egot
+ .hidden _end

__HEAD
.code32
--
2.24.1
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