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authorJeremy Compostella <jeremy.compostella@intel.com>2023-09-07 20:26:56 -0700
committerMatt DeVillier <matt.devillier@amd.corp-partner.google.com>2023-10-20 14:32:20 +0000
commit621ccf8a975de10a641ba36c9f8065b7fb659611 (patch)
tree85a7f3e5642a6cc3ea310ad03b9377aab11f9ea6 /src/soc/mediatek/mt8186/soc.c
parent7f1f2973c543b7b16ca98d39382eee060ee5ae0c (diff)
cbfstool: Skip relocation entries pointing to undefined symbol
The linker can make relocation entries of a symbol which has a value of zero point to the undefined symbol entry. It is permitted since when the symbol value is zero as the documentation of the relocation entry `r_info' field states: "If the index is STN_UNDEF, the undefined symbol index, the relocation uses 0 as the symbol value." The ELF binary does not really have any missing symbols. It is an optimization as the symbol points to the undefined symbol because its value is zero. A typical way to hit this cbfstool limitation is to define an empty region using the REGION macro in the linker script. Here is an example if we assume `CONFIG_MY_REGION' is set to 0: .car.data { [...] REGION(my_region, CONFIG_MY_REGION_SIZE) [...] } A region is defined as follow: #define REGION_SIZE(name) ((size_t)_##name##_size) #define DECLARE_REGION(name) \ extern u8 _##name[]; \ extern u8 _e##name[]; \ extern u8 _##name##_size[]; So the size of the region is actually the address of the `_##name##_size' symbol. Therefore, the `_my_region_size' symbol address is zero and the linker can make the relocation entry of this symbol point to the undefined symbol index. In such a situation, cbfstool hits a segmentation fault when it attempts to relocate the symbol in `parse_elf_to_xip_stage()' function. We resolves this issue by making cbfstool skips relocation entries pointing to the undefined symbol similarly to the way it skips relocation relative to absolute symbols. A symbol which value is zero can be considered an absolute symbol and therefore should not be relocated. Of course, we could argue that we could just prevent the declaration of an empty region as illustrated in the following example: .car.data { [...] #if CONFIG_MY_REGION_SIZE > 0 REGION(my_region, CONFIG_MY_REGION_SIZE) #endif [...] } However, this is not a satisfying solution because: 1. It requires to add unnecessary code in the linker script as an empty region is a valid declaration. Such a workaround requires the code using it to mark the region symbols as weak symbols to handle the situation where the region is not defined. 2. There could be other situations which have yet to be uncovered which would lead the same cbfstool crash. 3. A binary with an empty region is a valid ELF file and cbfstool should not crash when it is asked to create an eXecute-In-Place stage out of it. Change-Id: I2803fd3e96e7ff7a0b22d72d50bfbce7acaeb941 Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com> Reviewed-on: https://review.coreboot.org/c/coreboot/+/77699 Tested-by: build bot (Jenkins) <no-reply@coreboot.org> Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Diffstat (limited to 'src/soc/mediatek/mt8186/soc.c')
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