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| author | Ben Gamari <ben@smart-cactus.org> | 2019-12-02 12:48:23 -0500 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2019-12-02 13:16:40 -0500 |
| commit | c8a5e73efca10e431ed9b9bbb635f889bfc4103c (patch) | |
| tree | 7287decb4621aae1c28eb5d0e59b4a68821a604f | |
| parent | 3a96a0b6db6a32457ae2f91bb711c2481c767656 (diff) | |
| download | haskell-wip/fix-link-info-note.tar.gz | |
Elf: Fix link info note generationwip/fix-link-info-note
Previously we would use the `.int` assembler directive to generate
32-bit words in the note section. However, `.int` is note guaranteed to
produce 4-bytes; in fact, on some platforms (e.g. AArch64) it produces
8-bytes. Use the `.4bytes` directive to avoid this.
Moreover, we used the `.align` directive, which is quite platform
dependent. On AArch64 it appears to not even be idempotent (despite what
the documentation claims). `.balign` is consequentially preferred as it
offers consistent behavior across platforms.
| -rw-r--r-- | compiler/main/Elf.hs | 16 |
1 files changed, 4 insertions, 12 deletions
diff --git a/compiler/main/Elf.hs b/compiler/main/Elf.hs index 648f20aad9..9e19de12dd 100644 --- a/compiler/main/Elf.hs +++ b/compiler/main/Elf.hs @@ -408,15 +408,6 @@ readElfNoteAsString dflags path sectionName noteId = action `catchIO` \_ -> do -- | Generate the GAS code to create a Note section -- -- Header fields for notes are 32-bit long (see Note [ELF specification]). --- --- It seems there is no easy way to force GNU AS to generate a 32-bit word in --- every case. Hence we use .int directive to create them: however "The byte --- order and bit size of the number depends on what kind of target the assembly --- is for." (https://sourceware.org/binutils/docs/as/Int.html#Int) --- --- If we add new target platforms, we need to check that the generated words --- are 32-bit long, otherwise we need to use platform specific directives to --- force 32-bit .int in asWord32. makeElfNote :: String -> String -> Word32 -> String -> SDoc makeElfNote sectionName noteName typ contents = hcat [ text "\t.section ", @@ -424,6 +415,7 @@ makeElfNote sectionName noteName typ contents = hcat [ text ",\"\",", sectionType "note", text "\n", + text "\t.balign 4\n", -- note name length (+ 1 for ending \0) asWord32 (length noteName + 1), @@ -438,20 +430,20 @@ makeElfNote sectionName noteName typ contents = hcat [ text "\t.asciz \"", text noteName, text "\"\n", - text "\t.align 4\n", + text "\t.balign 4\n", -- note contents (.ascii to avoid ending \0) + padding text "\t.ascii \"", text (escape contents), text "\"\n", - text "\t.align 4\n"] + text "\t.balign 4\n"] where escape :: String -> String escape = concatMap (charToC.fromIntegral.ord) asWord32 :: Show a => a -> SDoc asWord32 x = hcat [ - text "\t.int ", + text "\t.4byte ", text (show x), text "\n"] |