[4/10] libs/libc/elf: Translate link-time addresses through one place.

[casaroli]

Summary

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 down picks between those two forms with an explicit test on datasec.

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 - datasec is textalloc for 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 the PRs that #19673 is being split into, so each can be reviewed on its own. [1/10] #19938 is withdrawn: the bug it described is not real, because a relocatable module already runs its constructors from crt0. [2/10] #19939 is merged. [3/10] #19940 is independent of this one and they can merge in any order. The rest are the FDPIC work itself, one subsystem each, and each is a no-op with CONFIG_FDPIC off: loader core [5/10] #19942, ARM relocations, the callback entry points, the exec() path, DT_NEEDED through dlopen(), then documentation and a board configuration.

Impact

None intended. Pure refactor, no behaviour change, no configuration change.

Testing

Built for mps3-an547:picostest, which is CONFIG_ELF with CONFIG_PIC.

There is no hardware for this series, so the runtime evidence is emulated. mps2-an500:xipfs runs the whole execute-in-place loader under QEMU with no board, and that is where the module load path is exercised.

[github-actions]

MemBrowse Memory Report

s698pm-dkit

• Code: .text +32 B (+0.0%, 363,584 B)
  No memory changes detected for:
• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• stm32-nucleo-f103rb

[xiaoxiang781216]

ci was fixed, please rebase your change to the last master. @casaroli