[Bug]: [GenFw] FindPrmHandler in Elf64Convert.c assumes symbol value is file offset

[kurtjd]

Is there an existing issue for this?

• I have searched existing issues

Current Behavior

When GenFw is ran with the --prm option, it will attempt to locate the PrmModuleExportDescriptor symbol as part of the ScanSections64 function call. Once found, it will pass its 'st_value' field value into FindPrmHandler as an offset to find the location of PRM handler symbols in the file, as seen here:

mu_basecore/BaseTools/Source/C/GenFw/Elf64Convert.c

Line 991 in 5498883

FindPrmHandler(Sym->st_value);

However, st_value does not necessarily represent the offset of a symbol in the file. It appears to actually represent the VMA of the symbol. For example, on my build, PrmModuleExportDescriptor is placed in the .data section, which has a VMA of 0x6000, but the .data section is actually at file offset 0x7000. So, when st_value is passed into FindPrmHandler, the function begins looking at offset 0x6000 for PRM handlers rather than 0x7000.

A potential fix (which works on my build) is to calculate the symbol offset by first finding the section header it belongs to using the symbol's st_shndx field. Then, subtract the section's address from the symbol's address before finally adding the section offset, like this:

STATIC
Elf64_Addr
GetSymValueOffset (
  Elf_Sym* Sym
  )
{
    Elf_Shdr* shdr = GetShdrByIndex(Sym->st_shndx);
    return (Sym->st_value - shdr->sh_addr) + shdr->sh_offset;
}

Thus, anytime a symbol's value is treated as an offset, this function should be used instead.

Expected Behavior

I expect GenFw, when ran with the --prm option, to locate PRM-related symbols in an ELF file regardless of what their VMA value is.

Steps To Reproduce

1. Write a sample PRM module, and pass the --prm option to GenFw in the sample module's INF file
2. Build UEFI FW using the CLANG100WIN/ARM toolchain
3. View the build log, and observe that GenFw will likely error out as it attempts to read garbage (in my case, it prints error message "FindPrmHandler: Number 255 is too high." as it thought there were over 25,000 PRM Handlers)

Build Environment

- OS(s): Windows 11
- Tool Chain(s): CLANG100WIN, arm-linker
- Targets Impacted: AARCH64 DEBUG (only target tested)

Version Information

Latest

Urgency

Low

Are you going to fix this?

I will fix it

Do you need maintainer feedback?

Maintainer feedback requested

Anything else?

This shows .data has a VMA that is not equal to its file offset:

This shows PrmModuleExportDescriptor has a symbol value of 0x6000 (since it's the first symbol in .data):

And this shows PrmModuleExportDescriptor actually has a file offset of 0x7000 (thus the symbol's value is not its offset):

[github-actions]

This issue has been automatically marked as stale because it has not had activity in 45 days. It will be closed if no further activity occurs within 7 days. Thank you for your contributions.

[github-actions]

This issue has been automatically been closed because it did not have any activity in 45 days and no follow up within 7 days after being marked stale. Thank you for your contributions.