src: start the .text section with an asm symbol #31981

gabrielschulhof · 2020-02-27T10:03:48Z

We create an object file in assembly which introduces the symbol
__node_text_start into the .text section and place the resulting
object file as the first file the linker encounters. We do this to
ensure that we can recognize the boundaries of the .text section when
attempting to establish the address range to map to large pages.

Additionally, we rename the section containing the remapping code from
.lpstub to lpstub so as to take advantage of the linker's feature
whereby it inserts the symbol __start_lpstub when the section's name
can be rendered as a valid C variable. We need this symbol in order to
avoid self-mapping the remapping code to large pages, because doing so
would cause the process to crash.

Checklist

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

This is an alternative to #31947.

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash.

gabrielschulhof · 2020-02-27T17:15:12Z

Removed now-unused extern char __executable_start;.

nodejs-github-bot · 2020-02-27T17:17:37Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29420/

suresh-srinivas · 2020-02-27T17:37:00Z

This looks good to me. I think __executable_start will also work but the problem was in the surrounding code that had been rewritten from before and not tested, it looks like you have fixed it with this check so we are looking at the right line in the maps file.
if (permission != "r-xp")

suresh-srinivas · 2020-02-27T17:51:39Z

In the original code that I wrote I also had a check
if (pathname == exename)
to make sure that even if the line was "r-xp", it was pointing to the nodejs executable. This check was an additional precaution to make sure that we were looking at the right line in the maps file.

I havent been following all the code modifications to this file but it has been broken at least twice due to improper restructuring. I dont know what Node.js policies are, but I think it would be good to have a list of owners for files or subsystems.

gabrielschulhof · 2020-02-27T21:34:47Z

@suresh-srinivas IINM the fact that a known Node.js symbol (like __executable_start or __node_text_start with this modification) resides within the mapping under scrutiny establishes that the mapping in fact contains executable code from the Node.js binary rather than a shared library.

gabrielschulhof · 2020-02-27T21:35:43Z

@suresh-srinivas it's a good sanity check though ...

bnoordhuis

LGTM in general but I suspect it's likely that:

./configure --enable-lto breaks it
as would turning on -Wl,--gc-sections (which we currently don't but could)

src/large_pages/node_large_page.cc

bnoordhuis · 2020-02-28T11:03:24Z

src/large_pages/node_text_start.S

@@ -0,0 +1,5 @@
+.text
+.align 0x2000


Good question, actually. I'm not sure we need it, because we end up snipping the front and the back off the .text if it doesn't align at 2MiB anyway, leaving the snipped-off bits on 4KiB pages.

Co-Authored-By: Ben Noordhuis <info@bnoordhuis.nl>

gabrielschulhof · 2020-02-28T19:36:41Z

@bnoordhuis AFAICT this works with --enable-lto. I used the flag and the resulting binary was able to find 9 large pages worth of text. I tested this with

GNU ld version 2.31.1-37.fc30 on Fedora 30
GNU ld (GNU Binutils for Ubuntu) 2.30 on Ubuntu 18.04

I'm hoping the linker will not drop the symbol because there is a reference to it, even if it's a weak reference.

nodejs-github-bot · 2020-03-02T22:55:45Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29508/

nodejs-github-bot · 2020-03-03T02:59:43Z

CI: https://ci.nodejs.org/job/node-test-pull-request/29510/

gabrielschulhof · 2020-03-03T04:29:10Z

https://ci.nodejs.org/job/node-test-pull-request/29510/ was yellow, so landing...

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash. PR-URL: #31981 Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>

gabrielschulhof · 2020-03-03T04:33:19Z

Landed in 987a673.

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash. PR-URL: #31981 Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>

lundibundi · 2020-03-03T19:33:46Z

Looks like this broke build with configure --ninja. It fails for me locally every time (It cannot find the node_text_start file during linking).

Also, there is recent CI failure:
#32046
https://github.com/nodejs/node/pull/32046/checks?check_run_id=482240372

c++ -fsanitize=address -pthread -rdynamic -m64 obj.target/node_text_start/src/large_pages/node_text_start.o -Wl,--whole-archive obj/libnode.a obj/tools/v8_gypfiles/libv8_base_without_compiler.a -Wl,--no-whole-archive -Wl,--whole-archive obj/deps/zlib/libzlib.a -Wl,--no-whole-archive -Wl,--whole-archive obj/deps/uv/libuv.a -Wl,--no-whole-archive -Wl,-z,noexecstack -Wl,--whole-archive obj/tools/v8_gypfiles/libv8_snapshot.a -Wl,--no-whole-archive -Wl,-z,relro -Wl,-z,now -Wl,--whole-archive,obj/deps/openssl/libopenssl.a -Wl,--no-whole-archive -pthread -o node -Wl,--start-group obj/gen/node.node_code_cache.o obj/gen/node.node_snapshot.o obj/src/node.node_main.o obj/deps/histogram/libhistogram.a obj/deps/uvwasi/libuvwasi.a obj/libnode.a obj/libnode_text_start.a obj/tools/v8_gypfiles/libv8_libplatform.a obj/tools/icu/libicui18n.a obj/deps/zlib/libzlib.a obj/deps/llhttp/libllhttp.a obj/deps/cares/libcares.a obj/deps/uv/libuv.a obj/deps/nghttp2/libnghttp2.a obj/deps/brotli/libbrotli.a obj/deps/openssl/libopenssl.a obj/tools/v8_gypfiles/libv8_base_without_compiler.a obj/tools/icu/libicuucx.a obj/tools/icu/libicudata.a obj/tools/v8_gypfiles/libv8_libbase.a obj/tools/v8_gypfiles/libv8_libsampler.a obj/tools/v8_gypfiles/libv8_compiler.a obj/tools/v8_gypfiles/libv8_snapshot.a obj/tools/v8_gypfiles/libv8_initializers.a  -lm -ldl -Wl,--end-group
c++: error: obj.target/node_text_start/src/large_pages/node_text_start.o: No such file or directory

richardlau · 2020-03-03T20:08:56Z

Looks like this broke build with configure --ninja. It fails for me locally every time (It cannot find the node_text_start file during linking).

Also, there is recent CI failure:
#32046
https://github.com/nodejs/node/pull/32046/checks?check_run_id=482240372

c++ -fsanitize=address -pthread -rdynamic -m64 obj.target/node_text_start/src/large_pages/node_text_start.o -Wl,--whole-archive obj/libnode.a obj/tools/v8_gypfiles/libv8_base_without_compiler.a -Wl,--no-whole-archive -Wl,--whole-archive obj/deps/zlib/libzlib.a -Wl,--no-whole-archive -Wl,--whole-archive obj/deps/uv/libuv.a -Wl,--no-whole-archive -Wl,-z,noexecstack -Wl,--whole-archive obj/tools/v8_gypfiles/libv8_snapshot.a -Wl,--no-whole-archive -Wl,-z,relro -Wl,-z,now -Wl,--whole-archive,obj/deps/openssl/libopenssl.a -Wl,--no-whole-archive -pthread -o node -Wl,--start-group obj/gen/node.node_code_cache.o obj/gen/node.node_snapshot.o obj/src/node.node_main.o obj/deps/histogram/libhistogram.a obj/deps/uvwasi/libuvwasi.a obj/libnode.a obj/libnode_text_start.a obj/tools/v8_gypfiles/libv8_libplatform.a obj/tools/icu/libicui18n.a obj/deps/zlib/libzlib.a obj/deps/llhttp/libllhttp.a obj/deps/cares/libcares.a obj/deps/uv/libuv.a obj/deps/nghttp2/libnghttp2.a obj/deps/brotli/libbrotli.a obj/deps/openssl/libopenssl.a obj/tools/v8_gypfiles/libv8_base_without_compiler.a obj/tools/icu/libicuucx.a obj/tools/icu/libicudata.a obj/tools/v8_gypfiles/libv8_libbase.a obj/tools/v8_gypfiles/libv8_libsampler.a obj/tools/v8_gypfiles/libv8_compiler.a obj/tools/v8_gypfiles/libv8_snapshot.a obj/tools/v8_gypfiles/libv8_initializers.a  -lm -ldl -Wl,--end-group
c++: error: obj.target/node_text_start/src/large_pages/node_text_start.o: No such file or directory

I think #32071 should fix it.

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash. PR-URL: #31981 Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash. PR-URL: nodejs#31981 Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>

targos · 2020-04-20T19:51:51Z

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

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash. Backport-PR-URL: nodejs#32092 PR-URL: nodejs#31981 Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>

We create an object file in assembly which introduces the symbol `__node_text_start` into the .text section and place the resulting object file as the first file the linker encounters. We do this to ensure that we can recognize the boundaries of the .text section when attempting to establish the address range to map to large pages. Additionally, we rename the section containing the remapping code from `.lpstub` to `lpstub` so as to take advantage of the linker's feature whereby it inserts the symbol `__start_lpstub` when the section's name can be rendered as a valid C variable. We need this symbol in order to avoid self-mapping the remapping code to large pages, because doing so would cause the process to crash. Backport-PR-URL: #32092 PR-URL: #31981 Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: David Carlier <devnexen@gmail.com> Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>

gabrielschulhof requested review from bnoordhuis, devnexen and lundibundi February 27, 2020 10:03

nodejs-github-bot added build Issues and PRs related to build files or the CI. c++ Issues and PRs that require attention from people who are familiar with C++. labels Feb 27, 2020

gabrielschulhof mentioned this pull request Feb 27, 2020

src: use _init as the start of large pages #31947

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fhinkel approved these changes Feb 27, 2020

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jasnell approved these changes Feb 27, 2020

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gabrielschulhof force-pushed the text-start-via-asm branch from f7f93c3 to 00787b5 Compare February 27, 2020 17:14

devnexen approved these changes Feb 27, 2020

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bnoordhuis approved these changes Feb 28, 2020

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Remove braces around single-statement if-body

174b6ba

Co-Authored-By: Ben Noordhuis <info@bnoordhuis.nl>

gabrielschulhof closed this Mar 3, 2020

gabrielschulhof deleted the text-start-via-asm branch March 3, 2020 04:34

gabrielschulhof mentioned this pull request Mar 3, 2020

[v10.x] Backport large pages to v10.x #31105

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codebytere mentioned this pull request Mar 3, 2020

v13.10.0 proposal #32027

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richardlau mentioned this pull request Mar 3, 2020

build: fix building with ninja #32071

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MylesBorins mentioned this pull request Mar 4, 2020

v13.10.1 proposal #32099

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targos added the backport-blocked-v12.x label Apr 20, 2020

targos added backported-to-v12.x and removed backport-blocked-v12.x labels Apr 25, 2020

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v12.17.0 release proposal #33197

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src: start the .text section with an asm symbol #31981

src: start the .text section with an asm symbol #31981

gabrielschulhof commented Feb 27, 2020

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src: start the .text section with an asm symbol #31981

src: start the .text section with an asm symbol #31981

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