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authorLudovic Courtès <ludo@gnu.org>2016-11-20 23:34:36 +0100
committerLudovic Courtès <ludo@gnu.org>2016-11-21 00:34:48 +0100
commit8eb790f368be5d7beac728e55093b6a3ea22328b (patch)
tree417159a7d780fd54850b78131f2c55a98d332b50 /guix/build
parent1845c2a4362c96d7feea3132f21aec34a607f855 (diff)
syscalls: Add 'c-struct-field-offset'.
* guix/build/syscalls.scm (define-c-struct-macro): New macro. (define-c-struct): Use it. (c-struct-field-offset): New macro.
Diffstat (limited to 'guix/build')
-rw-r--r--guix/build/syscalls.scm31
1 files changed, 31 insertions, 0 deletions
diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index c3832f6d48..85de47d26e 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -267,6 +267,29 @@ result is the alignment of the \"most strictly aligned component\"."
(align offset type0)
type0))))))
+(define-syntax define-c-struct-macro
+ (syntax-rules ()
+ "Define NAME as a macro that can be queried to get information about the C
+struct it represents. In particular:
+
+ (NAME field-offset FIELD)
+
+returns the offset in bytes of FIELD within the C struct represented by NAME."
+ ((_ name ((fields types) ...))
+ (define-c-struct-macro name
+ (fields ...) 0 ()
+ ((fields types) ...)))
+ ((_ name (fields ...) offset (clauses ...) ((field type) rest ...))
+ (define-c-struct-macro name
+ (fields ...)
+ (+ (align offset type) (type-size type))
+ (clauses ... ((_ field-offset field) (align offset type)))
+ (rest ...)))
+ ((_ name (fields ...) offset (clauses ...) ())
+ (define-syntax name
+ (syntax-rules (field-offset fields ...)
+ clauses ...)))))
+
(define-syntax define-c-struct
(syntax-rules ()
"Define SIZE as the size in bytes of the C structure made of FIELDS. READ
@@ -274,6 +297,8 @@ as a deserializer and WRITE! as a serializer for the C structure with the
given TYPES. READ uses WRAP-FIELDS to return its value."
((_ name size wrap-fields read write! (fields types) ...)
(begin
+ (define-c-struct-macro name
+ ((fields types) ...))
(define size
(struct-size 0 () types ...))
(define (write! bv offset fields ...)
@@ -281,6 +306,12 @@ given TYPES. READ uses WRAP-FIELDS to return its value."
(define* (read bv #:optional (offset 0))
(read-types wrap-fields bv offset (types ...) ()))))))
+(define-syntax-rule (c-struct-field-offset type field)
+ "Return the offset in BYTES of FIELD within TYPE, where TYPE is a C struct
+defined with 'define-c-struct' and FIELD is a field identifier. An
+expansion-time error is raised if FIELD does not exist in TYPE."
+ (type field-offset field))
+
;;;
;;; FFI.