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| author | Richard Earnshaw <rearnsha@arm.com> | 2003-10-04 10:18:33 +0000 |
|---|---|---|
| committer | Richard Earnshaw <rearnsha@gcc.gnu.org> | 2003-10-04 10:18:33 +0000 |
| commit | ece7fc1c597318c531778033f1e1a30cf4012783 (patch) | |
| tree | f5b296c92a0b9aad4a4156603a2dd8df18b78498 | |
| parent | 78e82bbe0b7adf406b7b55fb6af0054a57d304d4 (diff) | |
| download | gcc-ece7fc1c597318c531778033f1e1a30cf4012783.zip gcc-ece7fc1c597318c531778033f1e1a30cf4012783.tar.gz gcc-ece7fc1c597318c531778033f1e1a30cf4012783.tar.bz2 | |
extend.texi: Document how GCC estimates and relies on the size of an asm.
* doc/extend.texi: Document how GCC estimates and relies on the size
of an asm.
From-SVN: r72089
| -rw-r--r-- | gcc/ChangeLog | 5 | ||||
| -rw-r--r-- | gcc/doc/extend.texi | 20 |
2 files changed, 25 insertions, 0 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 187375d..ebc9864 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,8 @@ +2003-10-04 Richard Earnshaw <reanrsha@arm.com> + + * doc/extend.texi: Document how GCC estimates and relies on the size + of an asm. + 2003-10-04 Richard Sandiford <rsandifo@redhat.com> * config/mips/mips.c (mips_pad_arg_upward): Pad floating-point diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index ce31713..36fbd26 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -4136,6 +4136,26 @@ If you are writing a header file that should be includable in ISO C programs, write @code{__asm__} instead of @code{asm}. @xref{Alternate Keywords}. +@subsection Size of an @code{asm} + +Some targets require that GCC track the size of each instruction used in +order to generate correct code. Because the final length of an +@code{asm} is only known by the assembler, GCC must make an estimate as +to how big it will be. The estimate is formed by counting the number of +statements in the pattern of the @code{asm} and multiplying that by the +length of the longest instruction on that processor. Statements in the +@code{asm} are identified by newline characters and whatever statement +separator characters are supported by the assembler; on most processors +this is the `@code{;}' character. + +Normally, GCC's estimate is perfectly adequate to ensure that correct +code is generated, but it is possible to confuse the compiler if you use +pseudo instructions or assembler macros that expand into multiple real +instructions or if you use assembler directives that expand to more +space in the object file than would be needed for a single instruction. +If this happens then the assembler will produce a diagnostic saying that +a label is unreachable. + @subsection i386 floating point asm operands There are several rules on the usage of stack-like regs in |