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src: find .text section using dl_iterate_phdr #32244

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gabrielschulhof
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Use dl_iterate_phdr(3) to find the mapping containing
__node_text_start instead of parsing /proc/self/maps.

Signed-off-by: @gabrielschulhof

Checklist
  • make -j4 test (UNIX), or vcbuild test (Windows) passes
  • commit message follows commit guidelines

@nodejs-github-bot nodejs-github-bot added the c++ Issues and PRs that require attention from people who are familiar with C++. label Mar 13, 2020
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@bnoordhuis bnoordhuis left a comment

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LGTM % some minor (mostly style) issues.

src/large_pages/node_large_page.cc Show resolved Hide resolved
src/large_pages/node_large_page.cc Outdated Show resolved Hide resolved
src/large_pages/node_large_page.cc Outdated Show resolved Hide resolved
uintptr_t end = start + phdr->p_memsz;

if (dl_params->reference_sym >= start &&
dl_params->reference_sym <= end) {
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Just checking, is end inclusive or exclusive?

Aside: it looks like there's no real need for the dl_params->reference_sym field. This also works, wouldn't it?

auto reference_sym = reinterpret_cast<uintptr_t>(&__node_text_start);
if (reference_sym >= start && reference_sym <= end) {
  // ...
}

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@bnoordhuis the reference_sym field is being used both inside the dl_iterate_phdr callback and outside of it. I thought it best not to assign reinterpret_cast<uintptr_t>(&__node_text_start); to two different variables because, if the symbol changes in the future, they might get out of sync.

}
}
return 0;
}, &dl_params) == 1) {
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For legibility, it'd be better to hoist the lambda out of the function call:

auto callback = [](dl_phdr_info* info, size_t, void* data) -> int {
  // ...
};

if (1 == dl_iterate_phdr(callback, &dl_params)) {
  // ...
}

src/large_pages/node_large_page.cc Show resolved Hide resolved
Comment on lines +157 to +171
if (dl_params.start < dl_params.end) {
char* from = reinterpret_cast<char*>(hugepage_align_up(dl_params.start));
char* to = reinterpret_cast<char*>(hugepage_align_down(dl_params.end));
if (from < to) {
size_t pagecount = (to - from) / hps;
if (pagecount > 0) {
nregion.found_text_region = true;
nregion.from = from;
nregion.to = to;
nregion.total_hugepages = pagecount;
}
}
}
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@bnoordhuis I added some more sanity checks to ensure that we create a region that has proper offsets and > 0 page count.

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... or rather, that we consider the region to have been found only if it has proper offsets and >0 page count.

@gabrielschulhof
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@bnoordhuis I addressed your review comments and added some sanity checks wrt. your comment regarding inclusive/exclusive comparison.

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Gabriel Schulhof and others added 6 commits March 13, 2020 14:46
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Rebased in the hope that if fixes the "node ASAN" test.

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@gabrielschulhof
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@nodejs/collaborators sorry about the spam! Can this land without the "node ASAN" test? AFAICT it's failing for a lot of PRs.

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sorry about the spam! Can this land without the "node ASAN" test? AFAICT it's failing for a lot of PRs.

Yes. 👍

@addaleax addaleax added the author ready PRs that have at least one approval, no pending requests for changes, and a CI started. label Mar 15, 2020
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@nodejs/collaborators sorry about the spam! Can this land without the "node ASAN" test? AFAICT it's failing for a lot of PRs.

We dealt with Node ASAN fail in #32116. Not sure we should cherrypick the commit to master, since the PR is pretty ready to launch.

Also +1 for this PR to launch.

gabrielschulhof pushed a commit that referenced this pull request Mar 16, 2020
Use `dl_iterate_phdr(3)` to find the mapping containing
`__node_text_start` instead of parsing `/proc/self/maps`.

Signed-off-by: Gabriel Schulhof <[email protected]>
Co-Authored-By: Ben Noordhuis <[email protected]>
PR-URL: #32244
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: David Carlier <[email protected]>
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Landed in 25cb855.

@gabrielschulhof gabrielschulhof deleted the large-pages-use-dl_iterate_phdr branch March 16, 2020 05:43
BridgeAR pushed a commit that referenced this pull request Mar 17, 2020
Use `dl_iterate_phdr(3)` to find the mapping containing
`__node_text_start` instead of parsing `/proc/self/maps`.

Signed-off-by: Gabriel Schulhof <[email protected]>
Co-Authored-By: Ben Noordhuis <[email protected]>
PR-URL: #32244
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: David Carlier <[email protected]>
@MylesBorins MylesBorins mentioned this pull request Mar 19, 2020
MylesBorins pushed a commit that referenced this pull request Mar 24, 2020
Use `dl_iterate_phdr(3)` to find the mapping containing
`__node_text_start` instead of parsing `/proc/self/maps`.

Signed-off-by: Gabriel Schulhof <[email protected]>
Co-Authored-By: Ben Noordhuis <[email protected]>
PR-URL: #32244
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: David Carlier <[email protected]>
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targos commented Apr 22, 2020

Depends on the large pages change to land on v12.x

@targos targos removed author ready PRs that have at least one approval, no pending requests for changes, and a CI started. backport-blocked-v12.x labels Apr 25, 2020
targos pushed a commit to targos/node that referenced this pull request Apr 25, 2020
Use `dl_iterate_phdr(3)` to find the mapping containing
`__node_text_start` instead of parsing `/proc/self/maps`.

Signed-off-by: Gabriel Schulhof <[email protected]>
Co-Authored-By: Ben Noordhuis <[email protected]>
PR-URL: nodejs#32244
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: David Carlier <[email protected]>
targos pushed a commit that referenced this pull request Apr 28, 2020
Use `dl_iterate_phdr(3)` to find the mapping containing
`__node_text_start` instead of parsing `/proc/self/maps`.

Signed-off-by: Gabriel Schulhof <[email protected]>
Co-Authored-By: Ben Noordhuis <[email protected]>
PR-URL: #32244
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: David Carlier <[email protected]>
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7 participants