# [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C 8 messages from 2017-02-10 to 2017-02-19. Participants: Johannes Schindelin, Pranit Bauva, René Scharfe, Junio C Hamano. Thread: https://gitlist.dev/t/45101 ## Johannes Schindelin, 2017-02-10 14:20 Subject: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: URL: https://gitlist.dev/e/a1b9143bb29a8a5979dd733ed20161e6769b2b83.1486736391.git.johannes.schindelin%40gmx.de ``` It is curious that only MacOSX builds trigger an error about this, both GCC and Clang, but not Linux GCC nor Clang (see https://travis-ci.org/git/git/jobs/200182819#L1152 for details): builtin/bisect--helper.c:299:6: error: variable 'good_syn' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized] if (missing_good && !missing_bad && current_term && ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ builtin/bisect--helper.c:350:7: note: uninitialized use occurs here if (!good_syn) ^~~~~~~~ If you "re-roll" (or, as pointed out at the Contributors' Summit, better put: if you send another iteration of the patch series), please squash this fix in. Signed-off-by: Johannes Schindelin --- Based-On: pu at https://github.com/dscho/git Fetch-Base-Via: git fetch https://github.com/dscho/git pu Published-As: https://github.com/dscho/git/releases/tag/bisect--helper-fixup-v1 Fetch-It-Via: git fetch https://github.com/dscho/git bisect--helper-fixup-v1 builtin/bisect--helper.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c index 8cd6527bd1..614a85ffb5 100644 --- a/builtin/bisect--helper.c +++ b/builtin/bisect--helper.c @@ -280,7 +280,7 @@ static int bisect_next_check(const struct bisect_terms *terms, int missing_good = 1, missing_bad = 1, retval = 0; char *bad_ref = xstrfmt("refs/bisect/%s", terms->term_bad); char *good_glob = xstrfmt("%s-*", terms->term_good); - char *bad_syn, *good_syn; + char *bad_syn = NULL, *good_syn = NULL; if (ref_exists(bad_ref)) missing_bad = 0; base-commit: 6fa4b393c01a84c9adf2e2435fba6de13227eabf -- 2.11.1.windows.1 ``` ## Pranit Bauva, 2017-02-10 15:30 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: URL: https://gitlist.dev/e/CAFZEwPOo6RPKgf-FKL6GNPK2RDtw00%3DWvaBYMjeoZXX%2BwHkjwA%40mail.gmail.com In-Reply-To: ``` Hey Johannes, On Fri, Feb 10, 2017 at 7:50 PM, Johannes Schindelin wrote: > > It is curious that only MacOSX builds trigger an error about this, both > GCC and Clang, but not Linux GCC nor Clang (see > https://travis-ci.org/git/git/jobs/200182819#L1152 for details): > > builtin/bisect--helper.c:299:6: error: variable 'good_syn' is used > uninitialized whenever 'if' condition is true > [-Werror,-Wsometimes-uninitialized] > if (missing_good && !missing_bad && current_term && > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > builtin/bisect--helper.c:350:7: note: uninitialized use occurs here > if (!good_syn) > ^~~~~~~~ > > If you "re-roll" (or, as pointed out at the Contributors' Summit, better > put: if you send another iteration of the patch series), please squash > this fix in. > > Signed-off-by: Johannes Schindelin Thanks for making this fix! :) I will squash it in. Regards, Pranit Bauva ``` ## René Scharfe, 2017-02-10 20:47 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: <128b4de6-7b8e-27b9-414d-c6c6529cb491@web.de> URL: https://gitlist.dev/e/128b4de6-7b8e-27b9-414d-c6c6529cb491%40web.de In-Reply-To: ``` Am 10.02.2017 um 15:20 schrieb Johannes Schindelin: > It is curious that only MacOSX builds trigger an error about this, both > GCC and Clang, but not Linux GCC nor Clang (see > https://travis-ci.org/git/git/jobs/200182819#L1152 for details): > > builtin/bisect--helper.c:299:6: error: variable 'good_syn' is used > uninitialized whenever 'if' condition is true > [-Werror,-Wsometimes-uninitialized] > if (missing_good && !missing_bad && current_term && > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > builtin/bisect--helper.c:350:7: note: uninitialized use occurs here > if (!good_syn) > ^~~~~~~~ The only way that good_syn could be used in the if block is by going to the label finish, which does the following before returning: if (!bad_ref) free(bad_ref); if (!good_glob) free(good_glob); if (!bad_syn) free(bad_syn); if (!good_syn) free(good_syn); On Linux that code is elided completely -- freeing NULL is a no-op. I guess free(3) has different attributes on OS X and compilers don't dare to optimize it away there. So instead of calling free(3) only in the case when we did not allocate memory (which makes no sense and leaks) we should either call it in the opposite case, or (preferred) unconditionally, as it can handle the NULL case itself. Once that's fixed initialization will be required even on Linux. René ``` ## Johannes Schindelin, 2017-02-13 16:23 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: URL: https://gitlist.dev/e/alpine.DEB.2.20.1702131722350.3496%40virtualbox In-Reply-To: <128b4de6-7b8e-27b9-414d-c6c6529cb491@web.de> ``` Hi René, On Fri, 10 Feb 2017, René Scharfe wrote: > Am 10.02.2017 um 15:20 schrieb Johannes Schindelin: > > It is curious that only MacOSX builds trigger an error about this, both > > GCC and Clang, but not Linux GCC nor Clang (see > > https://travis-ci.org/git/git/jobs/200182819#L1152 for details): > > > > builtin/bisect--helper.c:299:6: error: variable 'good_syn' is used > > uninitialized whenever 'if' condition is true > > [-Werror,-Wsometimes-uninitialized] > > if (missing_good && !missing_bad && current_term && > > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > builtin/bisect--helper.c:350:7: note: uninitialized use occurs here > > if (!good_syn) > > ^~~~~~~~ > > The only way that good_syn could be used in the if block is by going to the > label finish, which does the following before returning: > > if (!bad_ref) > free(bad_ref); > if (!good_glob) > free(good_glob); > if (!bad_syn) > free(bad_syn); > if (!good_syn) > free(good_syn); > > On Linux that code is elided completely -- freeing NULL is a no-op. I guess > free(3) has different attributes on OS X and compilers don't dare to optimize > it away there. > > So instead of calling free(3) only in the case when we did not allocate memory > (which makes no sense and leaks) we should either call it in the opposite > case, or (preferred) unconditionally, as it can handle the NULL case itself. > Once that's fixed initialization will be required even on Linux. Exactly, free(NULL) is a no-op. The problem before this fixup was that good_syn was not initialized to NULL. Ciao, Dscho ``` ## René Scharfe, 2017-02-13 18:27 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: <74dfcffe-274c-7045-420a-95612394d66b@web.de> URL: https://gitlist.dev/e/74dfcffe-274c-7045-420a-95612394d66b%40web.de In-Reply-To: ``` Am 13.02.2017 um 17:23 schrieb Johannes Schindelin: > Hi René, > > On Fri, 10 Feb 2017, René Scharfe wrote: > >> Am 10.02.2017 um 15:20 schrieb Johannes Schindelin: >>> It is curious that only MacOSX builds trigger an error about this, both >>> GCC and Clang, but not Linux GCC nor Clang (see >>> https://travis-ci.org/git/git/jobs/200182819#L1152 for details): >>> >>> builtin/bisect--helper.c:299:6: error: variable 'good_syn' is used >>> uninitialized whenever 'if' condition is true >>> [-Werror,-Wsometimes-uninitialized] >>> if (missing_good && !missing_bad && current_term && >>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> builtin/bisect--helper.c:350:7: note: uninitialized use occurs here >>> if (!good_syn) >>> ^~~~~~~~ >> >> The only way that good_syn could be used in the if block is by going to the >> label finish, which does the following before returning: >> >> if (!bad_ref) >> free(bad_ref); >> if (!good_glob) >> free(good_glob); >> if (!bad_syn) >> free(bad_syn); >> if (!good_syn) >> free(good_syn); >> >> On Linux that code is elided completely -- freeing NULL is a no-op. I guess >> free(3) has different attributes on OS X and compilers don't dare to optimize >> it away there. >> >> So instead of calling free(3) only in the case when we did not allocate memory >> (which makes no sense and leaks) we should either call it in the opposite >> case, or (preferred) unconditionally, as it can handle the NULL case itself. >> Once that's fixed initialization will be required even on Linux. > > Exactly, free(NULL) is a no-op. The problem before this fixup was that > good_syn was not initialized to NULL. Strictly speaking: no. The value doesn't matter -- the free(3) calls above will be done with NULL regardless, due to the conditionals. Setting bad_syn and good_syn to an invalid pointer would have calmed the compiler just as well, and would have had no ill side effect (i.e. no invalid free(3) call). Initializing to NULL is still the correct thing to do, of course -- together with removing the conditionals (or at least the negations). But back to the topic of why the compilers on OS X didn't optimize out the free(3) calls with their conditionals. AFAICS no attributes are set for the function in stdlib.h of in glibc[1] or Darwin[2]. And I can't see any relevant option in config.mak.uname (e.g. -no-builtin). It's not terribly important, but does anyone know what prevents the elision of "if (!p) free(p);" on OS X? René [1] https://sourceware.org/git/?p=glibc.git;a=blob;f=stdlib/stdlib.h;h=292c6a2f053a2a578cd09d75307c26ed191e1c00;hb=b987917e6aa7ffe2fd74f0b6a989438e6edd0727 [2] https://opensource.apple.com/source/Libc/Libc-1158.30.7/include/stdlib.h.auto.html ``` ## Junio C Hamano, 2017-02-13 19:14 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: URL: https://gitlist.dev/e/xmqqinodewdr.fsf%40gitster.mtv.corp.google.com In-Reply-To: <74dfcffe-274c-7045-420a-95612394d66b@web.de> ``` René Scharfe writes: > Initializing to NULL is still the correct thing to do, of course -- > together with removing the conditionals (or at least the negations). So, let's give Pranit a concrete "here is what we want to see squashed in", while you guys discuss peculiarity with various platforms and their system headers, which admittedly is a more interesting tangent ;-) There are early returns with "goto finish" even before _syn variables are first assigned to, so they would need to be initialized to NULL. The other two get their initial values right at the beginning, so they are OK. builtin/bisect--helper.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c index 8cd6527bd1..6949e8e5ca 100644 --- a/builtin/bisect--helper.c +++ b/builtin/bisect--helper.c @@ -280,7 +280,7 @@ static int bisect_next_check(const struct bisect_terms *terms, int missing_good = 1, missing_bad = 1, retval = 0; char *bad_ref = xstrfmt("refs/bisect/%s", terms->term_bad); char *good_glob = xstrfmt("%s-*", terms->term_good); - char *bad_syn, *good_syn; + char *bad_syn = NULL, *good_syn = NULL; if (ref_exists(bad_ref)) missing_bad = 0; @@ -341,14 +341,10 @@ static int bisect_next_check(const struct bisect_terms *terms, } goto finish; finish: - if (!bad_ref) - free(bad_ref); - if (!good_glob) - free(good_glob); - if (!bad_syn) - free(bad_syn); - if (!good_syn) - free(good_syn); + free(bad_ref); + free(good_glob); + free(bad_syn); + free(good_syn); return retval; } ``` ## Pranit Bauva, 2017-02-13 19:34 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: URL: https://gitlist.dev/e/CAFZEwPNUXcNY9Qdz%3D_B7q2kQuaecPzJtTMGdv8YMUPEz2vnp8A%40mail.gmail.com In-Reply-To: ``` Hey Junio, On Tue, Feb 14, 2017 at 12:44 AM, Junio C Hamano wrote: > René Scharfe writes: > >> Initializing to NULL is still the correct thing to do, of course -- >> together with removing the conditionals (or at least the negations). > > So, let's give Pranit a concrete "here is what we want to see > squashed in", while you guys discuss peculiarity with various > platforms and their system headers, which admittedly is a more > interesting tangent ;-) > > There are early returns with "goto finish" even before _syn > variables are first assigned to, so they would need to be > initialized to NULL. The other two get their initial values > right at the beginning, so they are OK. > > builtin/bisect--helper.c | 14 +++++--------- > 1 file changed, 5 insertions(+), 9 deletions(-) > > diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c > index 8cd6527bd1..6949e8e5ca 100644 > --- a/builtin/bisect--helper.c > +++ b/builtin/bisect--helper.c > @@ -280,7 +280,7 @@ static int bisect_next_check(const struct bisect_terms *terms, > int missing_good = 1, missing_bad = 1, retval = 0; > char *bad_ref = xstrfmt("refs/bisect/%s", terms->term_bad); > char *good_glob = xstrfmt("%s-*", terms->term_good); > - char *bad_syn, *good_syn; > + char *bad_syn = NULL, *good_syn = NULL; > > if (ref_exists(bad_ref)) > missing_bad = 0; > @@ -341,14 +341,10 @@ static int bisect_next_check(const struct bisect_terms *terms, > } > goto finish; > finish: > - if (!bad_ref) > - free(bad_ref); > - if (!good_glob) > - free(good_glob); > - if (!bad_syn) > - free(bad_syn); > - if (!good_syn) > - free(good_syn); > + free(bad_ref); > + free(good_glob); > + free(bad_syn); > + free(good_syn); > return retval; > } This helps a lot ;) Thanks! Regards, Pranit Bauva ``` ## Junio C Hamano, 2017-02-19 02:06 Subject: Re: [PATCH] fixup! bisect--helper: `bisect_next_check` & bisect_voc shell function in C Message-ID: URL: https://gitlist.dev/e/xmqqa89jlyrh.fsf%40gitster.mtv.corp.google.com In-Reply-To: ``` Junio C Hamano writes: > ... > So, let's give Pranit a concrete "here is what we want to see > squashed in", while you guys discuss peculiarity with various > platforms and their system headers, which admittedly is a more > interesting tangent ;-) > > There are early returns with "goto finish" even before _syn > variables are first assigned to, so they would need to be > initialized to NULL. The other two get their initial values > right at the beginning, so they are OK. > > builtin/bisect--helper.c | 14 +++++--------- > 1 file changed, 5 insertions(+), 9 deletions(-) While we are waiting for the topic to be fixed, I've tentatively applied this on top to update 'pu', so Travis should now be happy with 'pu' on Mac, too. ```