[4/10] libs/libc/elf: Translate link-time addresses through one place. - #19941
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[4/10] libs/libc/elf: Translate link-time addresses through one place.#19941casaroli wants to merge 1 commit into
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The ET_DYN path computes run-time addresses from link-time ones in five places, each open-coding the arithmetic, and two of them disagree about how: libelf_relocatedyn() adds textalloc to a relocation's r_offset in one branch and subtracts datasec before adding datastart in the next, while the value translation a few lines further down picks between those two forms with an explicit test on datasec. Collect that into libelf_addr(), which makes the test once: an address below the data segment's link-time base belongs to text, anything at or above it to data. This changes nothing today. libelf_elfsize() sets segpad = datasec - (text_vaddr + textsize) and libelf_load() then places datastart = textalloc + textsize + segpad so datastart - datasec is textalloc, and the data branch reduces to textalloc + vaddr -- exactly what the text branch returns, and exactly what adding a single load bias did before. The two forms are the same arithmetic written twice. They stop being the same once text and data are placed independently, which is what an FDPIC object requires: its two PT_LOAD segments are relocated separately so that the read-only one can be mapped in place on the media while only the writable one is copied. Having the translation in one function is what makes that possible without auditing every open-coded expression again. Built for mps3-an547:picostest, which is CONFIG_ELF with CONFIG_PIC, and boots identically to the same configuration without this change. Assisted-by: Claude Opus 5 (1M context) <noreply@anthropic.com> Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
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Summary
The
ET_DYNpath computes run-time addresses from link-time ones in five places, each open-coding the arithmetic, and two of them disagree about how.libelf_relocatedyn()addstextallocto a relocation'sr_offsetin one branch and subtractsdatasecbefore addingdatastartin the next, while the value translation a few lines down picks between those two forms with an explicit test ondatasec.This collects that into
libelf_addr(), which makes the test once: an address below the data segment's link-time base belongs to text, anything at or above it to data.It changes nothing today.
datastart - datasecistextallocfor the way an object is placed now, so both forms reduce to the same arithmetic. They stop being the same once text and data are placed independently, which is what an FDPIC object requires, and having the translation in one function is what makes that possible without auditing every open-coded expression again.This is the fourth of ten PRs that #19673 is being split into, so each can be reviewed on its own. The first four have no FDPIC content at all and do not depend on each other, so they can merge in any order. The remaining six are the FDPIC work itself, one subsystem each, and each is a no-op with
CONFIG_FDPICoff: loader core, ARM relocations, the callback entry points, theexec()path,DT_NEEDEDthroughdlopen(), then documentation and a board configuration. The others are[1/10]#19938,[2/10]#19939 and[3/10]#19940.Impact
None intended. Pure refactor, no behaviour change, no configuration change.
Testing
Built for
mps3-an547:picostest, which isCONFIG_ELFwithCONFIG_PIC.tools/checkpatch.shpasses.Runtime evidence on real hardware follows tomorrow, on an RP2350.