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| author | Kaz Kylheku <kaz@kylheku.com> | 2015-01-12 22:33:32 -0800 |
|---|---|---|
| committer | Kaz Kylheku <kaz@kylheku.com> | 2015-01-12 22:33:32 -0800 |
| commit | 0343c6f32c5bd8335e88595cb9d23506625b2586 (patch) | |
| tree | fd166afd54a05efb0cb39aecfd02768da9d8153b /HACKING | |
| parent | 3e313905ec6f7680c1408b12051cb81d46150083 (diff) | |
| download | txr-0343c6f32c5bd8335e88595cb9d23506625b2586.tar.gz txr-0343c6f32c5bd8335e88595cb9d23506625b2586.tar.bz2 txr-0343c6f32c5bd8335e88595cb9d23506625b2586.zip | |
Fix for LLVM wchar_t literals not being four byte
aligned, affecting OS X port.
* configure: Detect a SIZEOF_WCHAR_T when detecting integer
type that will hold a pointer. In the lit_align test,
if we are on Apple Mac OSX, use a lit_align of 2,
so the logic kicks in for padding literals and handling
misalignment.
* lib.h (litptr): Add a case for LIT_ALIGN < 4 and
SIZEOF_WCHAR_T == 4. In this case we do the arithmetic
on the pointer using short *, and then convert to
wchar_t.
* HACKING: New section 2.4.3 about new wchar_t hack.
Diffstat (limited to 'HACKING')
| -rw-r--r-- | HACKING | 57 |
1 files changed, 31 insertions, 26 deletions
@@ -1,8 +1,3 @@ - Txr Internals Guide - Kaz Kylheku <kaz@kylheku.com> - -CONTENTS: - SECTION LINE 0. Overview 47 @@ -22,26 +17,27 @@ SECTION LINE 2.3 The COBJ type 288 2.4 Strings 305 2.4.1 Encapsulated C Strings 320 -2.4.2 Representation Hacks for 2 Byte wchar_t 364 - -3. Garbage Collection 423 -3.1 Root Pointers 441 -3.2 GC-safe Code 464 -3.2.1 Rule One: Full Initialization 490 -3.2.2 Rule Two: Make it Reachable 519 -3.3 Weak Reference Support 654 -3.4 Finalization 697 -3.5 Generational GC 721 -3.5.2 Representation of Generations 730 -3.5.3 Basic Algorithm 766 -3.5.4 Handling Backpointers 801 -3.5.5 Generational GC and Finalization 879 - -4. Debugging 908 -4.2. Debugging the Yacc-generated Parser 1039 -4.3. Debugging GC Issues 1052 -4.4 Object Breakpoint 1075 -4.5 Valgrind: Your Friend 1094 +2.4.2 Representation Hacks for 2-byte wchar_t 364 +2.4.3 Representation hacks for 4-byte wchar_t that is 2-byte aligned 422 + +3. Garbage Collection 432 +3.1 Root Pointers 450 +3.2 GC-safe Code 473 +3.2.1 Rule One: Full Initialization 499 +3.2.2 Rule Two: Make it Reachable 528 +3.3 Weak Reference Support 663 +3.4 Finalization 706 +3.5 Generational GC 730 +3.5.2 Representation of Generations 739 +3.5.3 Basic Algorithm 775 +3.5.4 Handling Backpointers 810 +3.5.5 Generational GC and Finalization 888 + +4. Debugging 917 +4.2. Debugging the Yacc-generated Parser 1048 +4.3. Debugging GC Issues 1061 +4.4 Object Breakpoint 1084 +4.5 Valgrind: Your Friend 1103 0. Overview @@ -361,7 +357,7 @@ string. Note that it is okay if garbage objects contain auto_str values, which refer to strings that no longer exist, because the garbage collector will recognize these pointers by their type tag and not use them. -2.4.2 Representation Hacks for 2 Byte wchar_t +2.4.2 Representation Hacks for 2-byte wchar_t On some systems (notably Cygwin), the wide character type wchar_t is only two bytes wide, and the alignment of string literals and arrays is two @@ -419,6 +415,15 @@ The wref macro hides the displacement of the first character: On a platform where this hack isn't needed, these w* macros are no-ops. +2.4.3 Representation hacks for 4-byte wchar_t that is 2-byte aligned + +On the LLVM compiler on OS X, I ran into the issue that although wchar_t +is four byte aligned, the compiler neglects to make wide string literals +four byte aligned. Cases occur of misaligned literals. + +The solution is to borrow some of the logic that is used for handling +two-byte wchar_t. The data is similarly padded, and an adjustment calculation +takes place similarly to recover the pointer. 3. Garbage Collection |