SPARC ABI Changes in GCC 3.4

GNU Project (original) (raw)

GCC 3.4 fixes several cases in which earlier releases would not follow the SPARC calling conventions. This document describes each fix and the kind of code it will affect. In each case, GCC 3.4 will not be binary compatible with earlier releases.

Most of the fixes are related to the handling of small structure and union types in 64-bit mode.

A. Small structure arguments and return values (1)

Affected ABI	64-bit
Conditions	A small structure is passed or returned in a register; and it contains a unique field of type float .
Old behavior	The register was odd-numbered.
New behavior	The register is even-numbered.
Example	struct s { float f; }; void g (struct s x); x is passed in floating-point register %f0, instead of %f1.

B. Small structure arguments and return values (2)

Affected ABI	64-bit
Conditions	A small structure is passed or returned in registers; its size in bytes is not a multiple of 8 and is greater than 8; its last field is of integral type; and its last but one field is smaller than a word.
Old behavior	The last used register was padded at the most significant end.
New behavior	The last used register is padded at the least significant end.
Example	struct s { float f; int i; int j; }; void g (struct s x); x is passed in several registers, which are laid out as follows: %f0 %o0 (high) %o0 (low) %o1 (high) %o1 (low) Old behavior f padding i padding j New behavior f padding i j padding

C. Small unions arguments and return values

Affected ABI	64-bit
Conditions	A small union is passed or returned in a register; and its size in bytes is less than 8.
Old behavior	The register was padded at the most significant end.
New behavior	The register is padded at the least significant end.
Example	union u { int i; float f; }; void g (union u x); x is passed in register %o0, which is laid out as follows: %o0 (high) %o0 (low) Old behavior padding i/f New behavior i/f padding

D. Small structure arguments (1)

Affected ABI	64-bit
Conditions	A small structure is passed past the 6th argument slot and prior to the last one; and it contains a complex floating-point field.
Old behavior	The complex floating-point field was passed on the stack.
New behavior	The complex floating-point field is passed in registers.
Example	struct s { _Complex float cf; }; void g (struct s x1, struct s x2, struct s x3, struct s x4, struct s x5, struct s x6, struct s x7); x7 is passed in floating-point registers %f12-%f13, instead of on the stack.

E. Small structure arguments (2)

Affected ABI	64-bit
Conditions	A small structure is passed past the 6th argument slot and prior to the last one; it contains a nested structure; and the nested structure contains a floating-point field.
Old behavior	The floating-point field was passed on the stack.
New behavior	The floating-point field is passed in registers.
Example	struct s { struct { double d; } ns; }; void g (struct s x1, struct s x2, struct s x3, struct s x4, struct s x5, struct s x6, struct s x7); x7 is passed in floating-point registers %f12-%f13, instead of on the stack.

F. Complex floating-point arguments and return values

Affected ABI	32-bit
Conditions	A complex floating-point value is passed to or returned from a function.
Old behavior	The complex floating-point value was passed or returned according to the following table: argument return value _Complex float integer registers integer registers _Complex double integer registers integer registers _Complex long double memory memory
New behavior	The complex floating-point value is passed or returned according to the following table: argument return value _Complex float memory floating-point registers _Complex double memory floating-point registers _Complex long double memory floating-point registers
Example	_Complex float g (void); The return value is returned in floating-point registers %f0-%f1, instead of registers %o0-%o1.

G. TI mode integral arguments (GCC extension)

Affected ABI	64-bit
Conditions	A TI mode integral value is passed to a function.
Old behavior	The TI mode integral value was not aligned on a 16-byte boundary in the parameter array.
New behavior	The TI mode integral value is aligned on a 16-byte boundary in the parameter array.
Example	typedef int TItype __attribute__ ((mode (TI))); void g (int x1, TItype x2); x2 is passed in registers %o2-%o3, instead of %o1-%o2.

H. Complex integral arguments (GCC extension) (1)

Affected ABI	32-bit
Conditions	A _Complex long long value is passed to a function.
Old behavior	The _Complex long long value was passed in registers.
New behavior	The _Complex long long value is passed in memory.
Example	void g (_Complex long long x1); x1 (its address) is passed in register %o0, instead of %o0-%o3.

I. Complex integral arguments (GCC extension) (2)

Affected ABI	64-bit
Conditions	A complex integral value is passed in registers.
Old behavior	Two consecutive registers were reserved, regardless of the size of the complex integral value.
New behavior	Only one register is reserved if the complex integral value can fit in a single register.
Example	void g (_Complex int x1, _Complex int x2); x2 is passed in register %o1, instead of %o2.