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[Emacs-diffs] master 27540be: Improve UBSan discussion in etc/DEBUG
From: |
Paul Eggert |
Subject: |
[Emacs-diffs] master 27540be: Improve UBSan discussion in etc/DEBUG |
Date: |
Mon, 22 Apr 2019 20:26:30 -0400 (EDT) |
branch: master
commit 27540be5c6265821d8197beeebb82113994c6b94
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>
Improve UBSan discussion in etc/DEBUG
* etc/DEBUG: Improve -gdwarf-N documentation.
Go into more detail about UndefinedBehaviorSanitizer.
---
etc/DEBUG | 40 +++++++++++++++++++++++++++-------------
1 file changed, 27 insertions(+), 13 deletions(-)
diff --git a/etc/DEBUG b/etc/DEBUG
index 7175538..836e820 100644
--- a/etc/DEBUG
+++ b/etc/DEBUG
@@ -181,10 +181,10 @@ Good luck!
** When you are trying to analyze failed assertions or backtraces, it
is essential to compile Emacs with flags suitable for debugging.
-With GCC 4.8 or later, you can invoke 'make' with CFLAGS="-O0 -g3".
-With older GCC, you can use CFLAGS="-O0 -g3 -gdwarf-4", replacing "4"
-by the highest version of DWARF that your compiler supports;
-with non-GCC compilers, "-O0 -g3" may be the best you can do.
+Although CFLAGS="-O0 -g3" often suffices with modern compilers,
+you may benefit further by using CFLAGS="-O0 -g3 -gdwarf-4", replacing
+"4" by the highest version of DWARF that your compiler supports;
+this is especially important for GCC versions older than 4.8.
With GCC and higher optimization levels such as -O2, the
-fno-omit-frame-pointer and -fno-crossjumping options are often
essential. The latter prevents GCC from using the same abort call for
@@ -917,13 +917,26 @@ setting the new-console option before running Emacs under
GDB:
** Running Emacs with undefined-behavior sanitization
-Building Emacs with undefined-behavior sanitization can help debug
-integer overflow and other undefined behavior in C code. To use
-UndefinedBehaviorSanitizer with GCC and similar compilers, append
-'-fsanitize=undefined' to CFLAGS, either when running 'configure' or
-running 'make'. For example:
+Building Emacs with undefined-behavior sanitization can help find
+several kinds of low-level problems in C code, including:
- ./configure CFLAGS='-O0 -g3 -fsanitize=undefined'
+ * Out-of-bounds access of many (but not all) arrays.
+ * Signed integer overflow, e.g., (INT_MAX + 1).
+ * Integer shifts by a negative or wider-than-word value.
+ * Misaligned pointers and pointer overflow.
+ * Loading a bool or enum value that is out of range for its type.
+ * Passing NULL to or returning NULL from a function requiring nonnull.
+ * Passing a size larger than the corresponding array to memcmp etc.
+ * Passing invalid values to some builtin functions, e.g., __builtin_clz (0).
+ * Reaching __builtin_unreachable calls (in Emacs, 'eassume' failure).
+
+To use UndefinedBehaviorSanitizer with GCC and similar compilers,
+append '-fsanitize=undefined' to CFLAGS, either when running
+'configure' or running 'make'. When supported, you can also specify
+'bound-strict' and 'float-cast-overflow'. For example:
+
+ ./configure \
+ CFLAGS='-O0 -g3 -fsanitize=undefined,bounds-strict,float-cast-overflow'
You may need to append '-static-libubsan' to CFLAGS if your version of
GCC is installed in an unusual location.
@@ -940,9 +953,10 @@ program.
** Running Emacs with address sanitization
Building Emacs with address sanitization can help debug memory-use
-problems. To use AddressSanitizer with GCC and similar compilers,
-append '-fsanitize=address' to CFLAGS, either when running 'configure'
-or running 'make'. Configure, build and run Emacs with
+problems, such as freeing the same object twice. To use
+AddressSanitizer with GCC and similar compilers, append
+'-fsanitize=address' to CFLAGS, either when running 'configure' or
+running 'make'. Configure, build and run Emacs with
ASAN_OPTIONS='detect_leaks=0' in the environment to suppress
diagnostics of minor memory leaks in Emacs. For example:
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