llvm-project/lld/ELF/MapFile.h

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//===- MapFile.h ------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef LLD_ELF_MAPFILE_H
#define LLD_ELF_MAPFILE_H
namespace lld {
namespace elf {
void writeMapFile();
[ELF] Add --why-extract= to query why archive members/lazy object files are extracted Similar to D69607 but for archive member extraction unrelated to GC. This patch adds --why-extract=. Prior art: GNU ld -M prints ``` Archive member included to satisfy reference by file (symbol) a.a(a.o) main.o (a) b.a(b.o) (b()) ``` -M is mainly for input section/symbol assignment <-> output section mapping (often huge output) and the information may appear ad-hoc. Apple ld64 ``` __Z1bv forced load of b.a(b.o) _a forced load of a.a(a.o) ``` It doesn't say the reference file. Arm's proprietary linker ``` Selecting member vsnprintf.o(c_wfu.l) to define vsnprintf. ... Loading member vsnprintf.o from c_wfu.l. definition: vsnprintf reference : _printf_a ``` --- --why-extract= gives the user the full data (which is much shorter than GNU ld -Map). It is easy to track a chain of references to one archive member with a one-liner, e.g. ``` % ld.lld main.o a_b.a b_c.a c.a -o /dev/null --why-extract=- | tee stdout reference extracted symbol main.o a_b.a(a_b.o) a a_b.a(a_b.o) b_c.a(b_c.o) b() b_c.a(b_c.o) c.a(c.o) c() % ruby -ane 'BEGIN{p={}}; p[$F[1]]=[$F[0],$F[2]] if $.>1; END{x="c.a(c.o)"; while y=p[x]; puts "#{y[0]} extracts #{x} to resolve #{y[1]}"; x=y[0] end}' stdout b_c.a(b_c.o) extracts c.a(c.o) to resolve c() a_b.a(a_b.o) extracts b_c.a(b_c.o) to resolve b() main.o extracts a_b.a(a_b.o) to resolve a ``` Archive member extraction happens before --gc-sections, so this may not be a live path under --gc-sections, but I think it is a good approximation in practice. * Specifying a file avoids output interleaving with --verbose. * Required `=` prevents accidental overwrite of an input if the user forgets `=`. (Most of compiler drivers' long options accept `=` but not ` `) Differential Revision: https://reviews.llvm.org/D109572
2021-09-21 00:52:30 +08:00
void writeWhyExtract();
void writeCrossReferenceTable();
void writeArchiveStats();
} // namespace elf
} // namespace lld
#endif