gcc는 특정 플랫폼에서 각 유형의 정렬을 어떻게 얻습니까?

Question

gcc의 소스에 하드 코딩되었거나 프로그래밍 방식으로 가져온 것입니까?

Answer 1

아치 관련 폴더에 하드 코드 된 것 같습니다. http://www.google.com/codesearch#Yj7Hz1ZInUg/trunk/gcc-4.2.1/gcc/config/sparc/sparc.h

SPARC

/* No data type wants to be aligned rounder than this. */ 
#define BIGGEST_ALIGNMENT (TARGET_ARCH64 ? 128 : 64) 

/* The best alignment to use in cases where we have a choice. */ 
#define FASTEST_ALIGNMENT 64 

...

/* Make strings word-aligned so strcpy from constants will be faster. */ 
#define CONSTANT_ALIGNMENT(EXP, ALIGN) \ 
    ((TREE_CODE (EXP) == STRING_CST  \ 
    && (ALIGN) < FASTEST_ALIGNMENT)  \ 
    ? FASTEST_ALIGNMENT : (ALIGN)) 

/* Make arrays of chars word-aligned for the same reasons. */ 
#define DATA_ALIGNMENT(TYPE, ALIGN)    \ 
    (TREE_CODE (TYPE) == ARRAY_TYPE    \ 
    && TYPE_MODE (TREE_TYPE (TYPE)) == QImode \ 
    && (ALIGN) < FASTEST_ALIGNMENT ? FASTEST_ALIGNMENT : (ALIGN)) 

과 같은 폴더에 sparc.c합니다.

일부 기본 정렬 규칙은 gcc/tree.c에 정의되어 있습니다. void의 경우 :

/* We are not going to have real types in C with less than byte alignment, 
    so we might as well not have any types that claim to have it. */ 
    TYPE_ALIGN (void_type_node) = BITS_PER_UNIT; 
    TYPE_USER_ALIGN (void_type_node) = 0; 

빌드 프로세스에서 gcc로 컴파일됩니다.

따라서 기본 정렬은 컴파일되지만 gcc 코드에서 TREE 유형 객체를 조작하여 변경할 수 있습니다.

UPDATE : 팔, MIPS, SPARC 용

/* Minimum size in bits of the largest boundary to which any 
    and all fundamental data types supported by the hardware 
    might need to be aligned. No data type wants to be aligned 
    rounder than this. 

    Pentium+ prefers DFmode values to be aligned to 64 bit boundary 
    and Pentium Pro XFmode values at 128 bit boundaries. */ 

#define BIGGEST_ALIGNMENT 128 

/* Decide whether a variable of mode MODE should be 128 bit aligned. */ 
#define ALIGN_MODE_128(MODE) \ 
((MODE) == XFmode || SSE_REG_MODE_P (MODE)) 

/* The published ABIs say that doubles should be aligned on word 
    boundaries, so lower the alignment for structure fields unless 
    -malign-double is set. */ 

/* ??? Blah -- this macro is used directly by libobjc. Since it 
    supports no vector modes, cut out the complexity and fall back 
    on BIGGEST_FIELD_ALIGNMENT. */ 
... 
#define BIGGEST_FIELD_ALIGNMENT 32 
... 
/* If defined, a C expression to compute the alignment given to a 
    constant that is being placed in memory. EXP is the constant 
    and ALIGN is the alignment that the object would ordinarily have. 
    The value of this macro is used instead of that alignment to align 
    the object. 

    If this macro is not defined, then ALIGN is used. 

    The typical use of this macro is to increase alignment for string 
    constants to be word aligned so that `strcpy' calls that copy 
    constants can be done inline. */ 

#define CONSTANT_ALIGNMENT(EXP, ALIGN) ix86_constant_alignment ((EXP), (ALIGN)) 

/* If defined, a C expression to compute the alignment for a static 
    variable. TYPE is the data type, and ALIGN is the alignment that 
    the object would ordinarily have. The value of this macro is used 
    instead of that alignment to align the object. 

    If this macro is not defined, then ALIGN is used. 

    One use of this macro is to increase alignment of medium-size 
    data to make it all fit in fewer cache lines. Another is to 
    cause character arrays to be word-aligned so that `strcpy' calls 
    that copy constants to character arrays can be done inline. */ 

#define DATA_ALIGNMENT(TYPE, ALIGN) ix86_data_alignment ((TYPE), (ALIGN)) 

/* If defined, a C expression to compute the alignment for a local 
    variable. TYPE is the data type, and ALIGN is the alignment that 
    the object would ordinarily have. The value of this macro is used 
    instead of that alignment to align the object. 

    If this macro is not defined, then ALIGN is used. 

    One use of this macro is to increase alignment of medium-size 
    data to make it all fit in fewer cache lines. */ 

#define LOCAL_ALIGNMENT(TYPE, ALIGN) ix86_local_alignment ((TYPE), (ALIGN)) 

... 

/* Set this nonzero if move instructions will actually fail to work 
    when given unaligned data. */ 
#define STRICT_ALIGNMENT 0 

및 정렬 아치에 기록 될 수있는 기계 명령어의 필요 (메모리에 정렬되지 않은 액세스를 제한하는) 다른 사람의 아치 : 86의 설정은 더 좋은 의견을 가지고있다. md 파일 (예 : sparc.md)