Skip to content

Commit b5de48f

Browse files
mikee47mikee47
committed
Use __asm__("name") consistently for IMPORT_FSTR
Using `extern "C"` within anonymous namespace is officially undefined behaviour. Underscores removed from assembler symbol names. This was only required on some platforms to accommodate `extern "C"`. New `DECLARE_FSTR_IMPORT` macro added.
1 parent d5ab318 commit b5de48f

4 files changed

Lines changed: 36 additions & 43 deletions

File tree

‎src/include/FlashString/Object.hpp‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -78,15 +78,15 @@
7878
*/
7979
#define IMPORT_FSTR_OBJECT(name, ObjectType, file) \
8080
IMPORT_FSTR_DATA(FSTR_DATA_NAME(name), file) \
81-
extern "C" __attribute__((visibility("hidden"))) const ObjectType ASM_LABEL(FSTR_DATA_NAME(name)); \
81+
__attribute__((visibility("hidden"))) DECLARE_FSTR_IMPORT(ObjectType, FSTR_DATA_NAME(name)); \
8282
DEFINE_FSTR_OBJREF(name, FSTR_DATA_NAME(name))
8383

8484
/**
8585
* @brief Like IMPORT_FSTR_OBJECT except reference is declared static constexpr
8686
*/
8787
#define IMPORT_FSTR_OBJECT_LOCAL(name, ObjectType, file) \
8888
IMPORT_FSTR_DATA(FSTR_DATA_NAME(name), file) \
89-
extern "C" __attribute__((visibility("hidden"))) const ObjectType ASM_LABEL(FSTR_DATA_NAME(name)); \
89+
__attribute__((visibility("hidden"))) DECLARE_FSTR_IMPORT(ObjectType, FSTR_DATA_NAME(name)); \
9090
static constexpr DEFINE_FSTR_OBJREF(name, FSTR_DATA_NAME(name))
9191

9292
namespace FSTR

‎src/include/FlashString/Utility.hpp‎

Lines changed: 33 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -79,49 +79,52 @@ template <typename T, typename U> struct argument_type<T(U)> {
7979
*
8080
* No C/C++ symbol is declared, this is type-dependent and must be done separately:
8181
*
82-
* extern "C" FSTR::String myFlashData;
82+
* DECLARE_FSTR_IMPORT(FSTR::String, myFlashData);
8383
*
8484
* If the symbol is not referenced the content will be discarded by the linker.
85+
*
8586
*/
8687
// clang-format off
8788
#define STR(x) XSTR(x)
8889
#define XSTR(x) #x
8990
#ifdef __WIN32
90-
#define IMPORT_FSTR_DATA(name, file) \
91-
__asm__(".section .rodata\n" \
92-
".def _" STR(name) "; .scl 2; .type 32; .endef\n" \
93-
".align 4\n" \
94-
"_" STR(name) ":\n" \
95-
".long _" STR(name) "_end - _" STR(name) " - 4\n" \
96-
".incbin \"" file "\"\n" \
97-
"_" STR(name) "_end:\n");
91+
#define IMPORT_FSTR_DATA_SECTION(name) \
92+
".section .rodata\n" \
93+
".def " STR(name) "; .scl 2; .type 32; .endef\n"
9894
#elif defined(__APPLE__)
99-
#define IMPORT_FSTR_DATA(name, file) \
100-
__asm__(".const_data\n" \
101-
".globl _" STR(name) "\n" \
102-
".align 4\n" "_" STR(name) ":\n" \
103-
".long _" STR(name) "_end - _" STR(name) " - 4\n" \
104-
".incbin \"" file "\"\n" \
105-
"_" STR(name) "_end:\n");
95+
#define IMPORT_FSTR_DATA_SECTION(name) \
96+
".const_data\n" \
97+
".globl " STR(name) "\n"
10698
#elif defined(__arm__)
107-
#define IMPORT_FSTR_DATA(name, file) \
108-
__asm__(".section " ICACHE_RODATA_SECTION "." STR(name) "\n" \
109-
".type " STR(name) ", %object\n" \
110-
".align 4\n" STR(name) ":\n" \
111-
".long _" STR(name) "_end - " STR(name) " - 4\n" \
112-
".incbin \"" file "\"\n" \
113-
"_" STR(name) "_end:\n");
99+
#define IMPORT_FSTR_DATA_SECTION(name) \
100+
".section " ICACHE_RODATA_SECTION "." STR(name) "\n" \
101+
".type " STR(name) ", %object\n"
114102
#else
115-
#define IMPORT_FSTR_DATA(name, file) \
116-
__asm__(".section " ICACHE_RODATA_SECTION "." STR(name) "\n" \
117-
".type " STR(name) ", @object\n" \
118-
".align 4\n" STR(name) ":\n" \
119-
".long _" STR(name) "_end - " STR(name) " - 4\n" \
120-
".incbin \"" file "\"\n" \
121-
"_" STR(name) "_end:\n");
103+
#define IMPORT_FSTR_DATA_SECTION(name) \
104+
".section " ICACHE_RODATA_SECTION "." STR(name) "\n" \
105+
".type " STR(name) ", @object\n"
122106
#endif
107+
108+
#define IMPORT_FSTR_DATA(name, file) \
109+
__asm__(IMPORT_FSTR_DATA_SECTION(name) \
110+
".align 4\n" \
111+
STR(name) ":\n" \
112+
".long " STR(name) "_end - " STR(name) " - 4\n" \
113+
".incbin \"" file "\"\n" \
114+
STR(name) "_end:\n");
123115
// clang-format on
124116

117+
/**
118+
* @brief Declare a reference to an `IMPORT_FSTR_DATA` block
119+
*
120+
* When referencing inline assembler labels using `extern "C"` tells the compiler
121+
* not to mangle the name. However, doing that inside an anonymous namespace leads
122+
* to undefined behaviour and breaks with GCC 15.
123+
* Using an explicit `asm(label)` directive makes this unambiguous.
124+
* See https://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html
125+
*/
126+
#define DECLARE_FSTR_IMPORT(ObjectType, name) extern const ObjectType name __asm__(STR(name));
127+
125128
namespace FSTR
126129
{
127130
/**

‎src/include/FlashString/config.hpp‎

Lines changed: 0 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -46,13 +46,3 @@
4646
*/
4747
#define ALIGNUP4(n) (((n) + 3) & ~3)
4848
#endif
49-
50-
/*
51-
When referencing inline assembler labels using `extern "C"` tells the compiler not to
52-
mangle the name. GCC 15 ignores this so requires an additional `asm(label)` directive.
53-
*/
54-
#if defined(__clang__) || defined(__WIN32)
55-
#define ASM_LABEL(name) name
56-
#else
57-
#define ASM_LABEL(name) name asm(STR(name))
58-
#endif

‎utility.rst‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -57,7 +57,7 @@ You'll need to define an appropriate symbol::
5757
uint8_t data[1024];
5858
};
5959

60-
extern "C" const MyCustomStruct myCustomData;
60+
DECLARE_FSTR_IMPORT(MyCustomStruct, myCustomData)
6161

6262
You'll still have to consider how the data is accessed. If it's small and un-complicated
6363
you can just copy it into RAM::

0 commit comments

Comments
 (0)