[LLVMdev] [PATCH v2] LangRef: clarify that va_arg doesn't work on x86_64 (original) (raw)

Ramkumar Ramachandra artagnon at gmail.com
Wed Oct 29 12:21:33 PDT 2014

Since x86_64 is easily the most popular platform, it deserves special mention. varargs on x86_64 probably requires a separate page.

Cc: Tim Northover <t.p.northover at gmail.com> Cc: Reid Kleckner <rnk at google.com> Signed-off-by: Ramkumar Ramachandra <artagnon at gmail.com>

docs/LangRef.rst | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/docs/LangRef.rst b/docs/LangRef.rst index ddef803..b288f9b 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -6695,7 +6695,8 @@ Overview: The 'va_arg' instruction is used to access arguments passed through the "variable argument" area of a function call. It is used to implement -the va_arg macro in C. +the va_arg macro in C. Note that va_arg does not work on +platforms that have a non-builtin va_list type, like x86_64. Arguments: """""""""" @@ -6879,8 +6880,10 @@ value type "va_list". The LLVM assembly language reference manual does not define what this type is, so all transformations should be prepared to handle these functions regardless of the type used. -This example shows how the :ref:va_arg <i_va_arg> instruction and the -variable argument handling intrinsic functions are used. +This example shows how the :ref:va_arg <i_va_arg> instruction and +the variable argument handling intrinsic functions are used. Note that +this is for platforms where va_list is an i8**, most notably +not x86_64. .. code-block:: llvm

1.9.3 (Apple Git-50)

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