[all-commits] [llvm/llvm-project] 172840: [LLD][ELF][RISCV][Zicfilp] Handle .note.gnu.proper...

[Ming-Yi Lai via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1728405b13781f2e2696ed2679c9d05101116fa2
      https://github.com/llvm/llvm-project/commit/1728405b13781f2e2696ed2679c9d05101116fa2
  Author: Ming-Yi Lai <ming-yi.lai at mediatek.com>
  Date:   2025-06-06 (Fri, 06 Jun 2025)

  Changed paths:
    M lld/ELF/Config.h
    M lld/ELF/Driver.cpp
    M lld/ELF/InputFiles.cpp
    M lld/ELF/SyntheticSections.cpp
    A lld/test/ELF/riscv-feature-zicfilp-func-sig.s
    A lld/test/ELF/riscv-feature-zicfilp-unlabeled.s
    A lld/test/ELF/riscv-feature-zicfiss.s

  Log Message:
  -----------
  [LLD][ELF][RISCV][Zicfilp] Handle .note.gnu.property sections for Zicfilp/Zicfiss features (#127193)

+ When all relocatable files contain a `.note.gnu.property` section
(with `NT_GNU_PROPERTY_TYPE_0` notes) which contains a
`GNU_PROPERTY_RISCV_FEATURE_1_AND` property in which the
`GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_UNLABELED`/`GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_FUNC_SIG`/`GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_SS`
bit is set:
  + The output file will contain a `.note.gnu.property` section with the
bit set
  + A `PT_GNU_PROPERTY` program header is created to encompass the
`.note.gnu.property` section
+ If `-z zicfilp-unlabeled-report=[warning|error]`/`-z
zicfilp-func-sig-report=[warning|error]`/`-z
zicfiss-report=[warning|error]` is specified, the linker will report a
warning or error for any relocatable file lacking the feature bit

RISC-V Zicfilp/Zicfiss features indicate their adoptions as bits in the
`.note.gnu.property` section of ELF files. This patch enables LLD to
process the information correctly by parsing, checking and merging the
bits from all input ELF files and writing the merged result to the
output ELF file.

These feature bits are encoded as a mask in each input ELF files and
intended to be "and"-ed together to check that all input files support a
particular feature.

For RISC-V Zicfilp features, there are 2 conflicting bits allocated:
`GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_UNLABELED` and
`GNU_PROPERTY_RISCV_FEATURE_1_CFI_LP_FUNC_SIG`. They represent the
adoption of the forward edge protection of control-flow integrity with
the "unlabeled" or "func-sig" policy. Since these 2 policies conflicts
with each other, these 2 bits also conflict with each other. This patch
adds the `-z zicfilp-unlabeled-report=[none|warning|error]` and `-z
zicfilp-func-sig-report=[none|warning|error]` commandline options to
make LLD report files that do not have the expected bits toggled on.

For RISC-V Zicfiss feature, there's only one bit allocated:
`GNU_PROPERTY_RISCV_FEATURE_1_CFI_SS`. This bit indicates that the ELF
file supports Zicfiss-based shadow stack. This patch adds the `-z
zicfiss-report=[none|warning|error]` commandline option to make LLD
report files that do not have the expected bit toggled on.

The adoption of the `.note.gnu.property` section for RISC-V targets can
be found in the psABI PR
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/417>
(`CFI_LP_UNLABELED` and `CFI_SS`) and PR
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/434>
(`CFI_LP_FUNC_SIG`).



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