[BOLT] Add reading support for Linux kernel .altinstructions section #84283
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Read .altinstructions and annotate instructions that have alternative sequences with "AltInst" annotation. Note that some instructions may have more than one alternatives, in which case they will have multiple annotations in the form "AltInst", "AltInst2", "AltInst3", etc.
maksfb
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aaupov,
rafaelauler,
ayermolo and
dcci
as code owners
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Need to add a test case. |
dcci
reviewed
Mar 7, 2024
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| static cl::opt<bool> | ||
| DumpAltInstructions("dump-alt-instructions", | ||
| cl::desc("dump Linux alernative instructions info"), |
dcci
reviewed
Mar 7, 2024
| DataExtractor::Cursor Cursor(0); | ||
| while (Cursor && !DE.eof(Cursor)) { | ||
| const uint64_t OrgInstAddress = | ||
| Address + Cursor.tell() + (int32_t)DE.getU32(Cursor); |
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here you're parsing a signed 32-bit value as unsigned then casting. Is it always correct?
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Yes. That's what DataExtractor::getSigned() does underneath. I would have used it, but there's no Cursor version of this interface.
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Doesn't coding guide prefers using c++ style casting?
https://llvm.org/docs/CodingStandards.html#prefer-c-style-casts
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The rule lists an exception for integral type casts.
dcci
reviewed
Mar 7, 2024
| /// struct alt_instr { | ||
| /// s32 instr_offset; | ||
| /// s32 repl_offset; | ||
| /// uXX feature; |
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u16 or u32. Perhaps u64 in the future.
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dcci
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Mar 7, 2024
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Thanks for the review. |
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Read .altinstructions and annotate instructions that have alternative sequences with "AltInst" annotation. Note that some instructions may have more than one alternatives, in which case they will have multiple annotations in the form "AltInst", "AltInst2", "AltInst3", etc.