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diff: ensure correct lifetime of external_diff_cmd #2026

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merged 1 commit into from
Jan 16, 2019

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@kgybels kgybels commented Jan 15, 2019

According to getenv(3)'s notes:

The implementation of getenv() is not required to be reentrant.  The
string pointed to by the return value of getenv() may be statically
allocated, and can be modified by a subsequent call to getenv(),
putenv(3), setenv(3), or unsetenv(3).

Since strings returned by getenv() are allowed to change on subsequent
calls to getenv(), make sure to duplicate when caching external_diff_cmd
from environment.

This problem becomes apparent on Git for Windows since fe21c6b
(mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8)),
when the getenv() implementation provided in compat/mingw.c was changed
to keep a certain amount of alloc'ed strings and freeing them on
subsequent calls.

This fixes #2007:

$ yes n | git -c difftool.prompt=yes difftool fe21c6b285df fe21c6b285df~100

Viewing (1/404): '.gitignore'
Launch 'bc3' [Y/n]?
Viewing (2/404): 'Documentation/.gitignore'
Launch 'bc3' [Y/n]?
Viewing (3/404): 'Documentation/Makefile'
Launch 'bc3' [Y/n]?
Viewing (4/404): 'Documentation/RelNotes/2.14.5.txt'
Launch 'bc3' [Y/n]?
Viewing (5/404): 'Documentation/RelNotes/2.15.3.txt'
Launch 'bc3' [Y/n]?
Viewing (6/404): 'Documentation/RelNotes/2.16.5.txt'
Launch 'bc3' [Y/n]?
Viewing (7/404): 'Documentation/RelNotes/2.17.2.txt'
Launch 'bc3' [Y/n]?
Viewing (8/404): 'Documentation/RelNotes/2.18.1.txt'
Launch 'bc3' [Y/n]?
Viewing (9/404): 'Documentation/RelNotes/2.19.0.txt'
Launch 'bc3' [Y/n]? error: cannot spawn ¦?: No such file or directory
fatal: external diff died, stopping at Documentation/RelNotes/2.19.1.txt

According to getenv(3)'s notes:

    The implementation of getenv() is not required to be reentrant.  The
    string pointed to by the return value of getenv() may be statically
    allocated, and can be modified by a subsequent call to getenv(),
    putenv(3), setenv(3), or unsetenv(3).

Since strings returned by getenv() are allowed to change on subsequent
calls to getenv(), make sure to duplicate when caching external_diff_cmd
from environment.

This problem becomes apparent on Git for Windows since fe21c6b
(mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8)),
when the getenv() implementation provided in compat/mingw.c was changed
to keep a certain amount of alloc'ed strings and freeing them on
subsequent calls.

This fixes git-for-windows#2007:

    $ yes n | git -c difftool.prompt=yes difftool fe21c6b fe21c6b~100

    Viewing (1/404): '.gitignore'
    Launch 'bc3' [Y/n]?
    Viewing (2/404): 'Documentation/.gitignore'
    Launch 'bc3' [Y/n]?
    Viewing (3/404): 'Documentation/Makefile'
    Launch 'bc3' [Y/n]?
    Viewing (4/404): 'Documentation/RelNotes/2.14.5.txt'
    Launch 'bc3' [Y/n]?
    Viewing (5/404): 'Documentation/RelNotes/2.15.3.txt'
    Launch 'bc3' [Y/n]?
    Viewing (6/404): 'Documentation/RelNotes/2.16.5.txt'
    Launch 'bc3' [Y/n]?
    Viewing (7/404): 'Documentation/RelNotes/2.17.2.txt'
    Launch 'bc3' [Y/n]?
    Viewing (8/404): 'Documentation/RelNotes/2.18.1.txt'
    Launch 'bc3' [Y/n]?
    Viewing (9/404): 'Documentation/RelNotes/2.19.0.txt'
    Launch 'bc3' [Y/n]? error: cannot spawn ¦?: No such file or directory
    fatal: external diff died, stopping at Documentation/RelNotes/2.19.1.txt

Signed-off-by: Kim Gybels <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>
@dscho dscho merged commit 4d3be1d into git-for-windows:master Jan 16, 2019
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dscho commented Jan 16, 2019

Thank you!!!

dscho added a commit to git-for-windows/build-extra that referenced this pull request Jan 16, 2019
A problem with `difftool` and more than a handful modified files
[has been fixed](git-for-windows/git#2026).

Signed-off-by: Johannes Schindelin <[email protected]>
@dscho dscho added this to the v2.20.1(2) milestone Jan 16, 2019
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dscho added a commit to dscho/git that referenced this pull request Feb 7, 2019
…-save-env

diff: ensure correct lifetime of external_diff_cmd
@gitster gitster deleted the kg/external-diff-save-env branch August 16, 2019 20:19
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Unable to Use difftool on More than 8 Files
3 participants