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