82 lines
3.2 KiB
Diff
82 lines
3.2 KiB
Diff
From 85ba5664eb368eb1cbd2c30b7cd574acd75edd4c Mon Sep 17 00:00:00 2001
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From: Niklas Cassel <niklas.cassel@wdc.com>
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Date: Mon, 4 Apr 2022 15:30:24 +0200
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Subject: [PATCH] elf2flt.ld: reinstate 32 byte alignment for .data section
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Commit 8a3e74446fe7 ("allow to build arm flat binaries") moved the
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following commands:
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. = ALIGN(0x20) ;
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@SYMBOL_PREFIX@_etext = . ;
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from the .text section to the top level in the SECTIONS node.
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The .text output section is being directed to a memory region using the
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"> flatmem :text" output section attribute. Commands in the top level in
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the SECTIONS node are not.
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This means that the ALIGN() command is no longer being appended to the
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flatmem memory region, it will simply update the Location Counter.
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The heuristic for placing an output section is described here:
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https://sourceware.org/binutils/docs-2.38/ld.html#Output-Section-Address
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"If an output memory region is set for the section then it is added to this
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region and its address will be the next free address in that region."
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Since the .data section is being directed to the same memory region as the
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.text section, this means that the Location Counter is not used when
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assigning an address to the .data output section, it will simply use the
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next free address.
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No longer directing these commands to the flatmem memory region means that
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the .data output section is no longer aligned to a 32 byte boundary.
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Before commit 8a3e74446fe7 ("allow to build arm flat binaries"):
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$ readelf -S busybox_unstripped.gdb | grep data
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[ 3] .data PROGBITS 0000000000035ac0 00036ac0
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$ readelf -s busybox_unstripped.gdb | grep _etext
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19286: 0000000000035ac0 0 NOTYPE GLOBAL DEFAULT 1 _etext
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After commit 8a3e74446fe7 ("allow to build arm flat binaries"):
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$ readelf -S busybox_unstripped.gdb | grep data
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[ 3] .data PROGBITS 0000000000035ab0 00036ab0
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$ readelf -s busybox_unstripped.gdb | grep _etext
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19287: 0000000000035ac0 0 NOTYPE GLOBAL DEFAULT 3 _etext
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The .data output section has to be aligned to a 32 byte boundary, see the
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FLAT_DATA_ALIGN 0x20 macro and its usage in fs/binfmt_flat.c:
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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/binfmt_flat.c?h=v5.17#n59
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Readd an explicit ALIGN attribute on the .data section itself, since the
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linker will obey this attribute regardless if being directed to a memory
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region or not. Also remove the ALIGN() command before the .data section,
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since this misleads the reader to think that the Location Counter is used
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when assigning an address to the .data section, when it actually is not.
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Fixes: 8a3e74446fe7 ("allow to build arm flat binaries")
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Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
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---
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elf2flt.ld.in | 5 +----
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1 file changed, 1 insertion(+), 4 deletions(-)
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diff --git a/elf2flt.ld.in b/elf2flt.ld.in
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index 0df999d..e5aea14 100644
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--- a/elf2flt.ld.in
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+++ b/elf2flt.ld.in
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@@ -94,12 +94,9 @@ W_RODAT: *(.gnu.linkonce.r*)
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*(.ARM.exidx* .gnu.linkonce.armexidx.*)
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} > flatmem
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@SYMBOL_PREFIX@__exidx_end = .;
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-
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- . = ALIGN(0x20) ;
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@SYMBOL_PREFIX@_etext = . ;
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- .data : {
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- . = ALIGN(0x4) ;
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+ .data ALIGN(0x20): {
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@SYMBOL_PREFIX@_sdata = . ;
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@SYMBOL_PREFIX@__data_start = . ;
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@SYMBOL_PREFIX@data_start = . ;
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--
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2.35.1
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