From ca678535c64570add58cfff95709c3c67384139d Mon Sep 17 00:00:00 2001 From: Johannes Schindelin Date: Mon, 5 Sep 2016 04:15:36 -0500 Subject: [PATCH] Demonstrate a problem: our pickaxe code assumes NUL-terminated buffers When our pickaxe code feeds file contents to regexec(), it implicitly assumes that the file contents are read into implicitly NUL-terminated buffers (i.e. that we overallocate by 1, appending a single '\0'). This is not so. In particular when the file contents are simply mmap()ed, we can be virtually certain that the buffer is preceding uninitialized bytes, or invalid pages. Note that the test we add here is known to be flakey: we simply cannot know whether the byte following the mmap()ed ones is a NUL or not. Typically, on Linux the test passes. On Windows, it fails virtually every time due to an access violation (that's a segmentation fault for you Unix-y people out there). And Windows would be correct: the regexec() call wants to operate on a regular, NUL-terminated string, there is no NUL in the mmap()ed memory range, and it is undefined whether the next byte is even legal to access. When run with --valgrind it demonstrates quite clearly the breakage, of course. So we simply mark it with `test_expect_success` for now. This test case represents a Minimal, Complete and Verifiable Example of a breakage reported by Chris Sidi. Signed-off-by: Johannes Schindelin --- t/t4059-diff-pickaxe.sh | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) create mode 100755 t/t4059-diff-pickaxe.sh diff --git a/t/t4059-diff-pickaxe.sh b/t/t4059-diff-pickaxe.sh new file mode 100755 index 0000000000..f0bf50bda7 --- /dev/null +++ b/t/t4059-diff-pickaxe.sh @@ -0,0 +1,22 @@ +#!/bin/sh +# +# Copyright (c) 2016 Johannes Schindelin +# + +test_description='Pickaxe options' + +. ./test-lib.sh + +test_expect_success setup ' + test_commit initial && + printf "%04096d" 0 >4096-zeroes.txt && + git add 4096-zeroes.txt && + test_tick && + git commit -m "A 4k file" +' +test_expect_success '-G matches' ' + git diff --name-only -G "^0{4096}$" HEAD^ >out && + test 4096-zeroes.txt = "$(cat out)" +' + +test_done