Changes to symbol visibility between RVCT v3.1 for µVision and RVCT v4.0 for µVision

ARM Compiler toolchain v5.02 for µVision Migration and Compatibility

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Changes to symbol visibility between RVCT v3.1 for µVision and RVCT v4.0 for µVision

The following changes to symbol visibility have been made:

Change to ELF visibility used to represent `__declspec(dllexport)`

When using the --hide_all compiler command-line option, which is the default, the ELF visibility used to represent __declspec(dllexport) in RVCT v3.1 for µVision and earlier was STV_DEFAULT. In RVCT v4.0 for µVision it is STV_PROTECTED. Symbols that are STV_PROTECTED can be referred to by other DLLs but cannot be preempted at load-time.

When using the --no_hide_all command-line option, the visibility of imported and exported symbols is still STV_DEFAULT as it was in RVCT v3.1for µVision.

`__attribute(visibility(...))`

The GNU-style __attribute(visibility(...)) has been added and is available even without specifying the --gnu compiler command-line option. Using it overrides any implicit visibility. For example, the following results in STV_DEFAULT visibility instead of STV_HIDDEN:

    __declspec(visibilty("default")) int x = 42;

RVCT v3.1 for µVision symbol visibility summary

The following tables summarize the visibility rules in RVCT v3.1 for µVision:

Table 1. RVCT v3.1 for µVision symbol visibility summary

Code	`--hide_all` (default)	`--no_hide_all`	`--dllexport_all`
`extern int x;` `extern int g(void);`	STV_HIDDEN	STV_DEFAULT	STV_HIDDEN
`extern int y = 42;` `extern int f() { return g() + x; }`	STV_HIDDEN	STV_DEFAULT	STV_DEFAULT
`__declspec(dllimport) extern int imx;` `__declspec(dllimport) extern int img(void);`	STV_DEFAULT	STV_DEFAULT	STV_DEFAULT
`__declspec(dllexport) extern int exy = 42;` `__declspec(dllexport) extern int exf() { return img() + imx; }`	STV_DEFAULT	STV_DEFAULT	STV_DEFAULT
`/* exporting undefs (unusual?) */` `__declspec(dllexport) extern int exz;` `__declspec(dllexport) extern int exh(void);`	STV_HIDDEN	STV_HIDDEN	STV_HIDDEN

Table 2. RVCT v3.1 for µVision symbol visibility summary for references to run-time functions

Code

--no_dllimport_runtime

--hide_all (default)

--no_hide_all

--dllexport_all

/* references to runtime functions, for

example __aeabi_fmul */

float fn(float a, float b) { return a*b; }

STV_HIDDEN

STV_DEFAULT

RVCT v4.0 for µVision symbol visibility summary

The following tables summarize the visibility rules in RVCT v4.0 for µVision:

Table 3. RVCT v4.0 for µVision symbol visibility summary

Code	`--hide_all` (default)	`--no_hide_all`	`--dllexport_all`
`extern int x;` `extern int g(void);`	STV_HIDDEN	STV_DEFAULT	STV_HIDDEN
`extern int y = 42;` `extern int f() { return g() + x; }`	STV_HIDDEN	STV_DEFAULT	STV_PROTECTED
`__declspec(dllimport) extern int imx;` `__declspec(dllimport) extern int img(void);`	STV_DEFAULT	STV_DEFAULT	STV_DEFAULT
`__declspec(dllexport) extern int exy = 42;` `__declspec(dllexport) extern int exf() { return img() + imx; }`	STV_PROTECTED	STV_PROTECTED	STV_PROTECTED
`/* exporting undefs (unusual?) */` `__declspec(dllexport) extern int exz;` `__declspec(dllexport) extern int exh(void);`	STV_PROTECTED	STV_PROTECTED	STV_PROTECTED

Table 4. RVCT v4.0 for µVision symbol visibility summary for references to run-time functions

Code

--no_dllimport_runtime

--hide_all (default)

--no_hide_all

--dllexport_all

/* references to runtime functions, for

example __aeabi_fmul */

float fn(float a, float b) { return a*b; }

STV_HIDDEN

STV_DEFAULT

Changes to symbol visibility between RVCT v3.1 for µVision and RVCT v4.0 for µVision