Hi all, I decided to investigate #1377, and while I wasn't able to reproduce it yet, on 32 bits GNU Hurd I got a segfault due to there being no result size calculation for "enum" foreign types. I discovered that if the type is unknown, the result size is assumed to be zero, so the generate C stub function receives C_SCHEME_UNDEFINED as a "buffer" (see core.scm:1815).
This is obviously not big enough to hold a bignum that might be returned from an enum on 32-bit systems, thus we're scribbling into unmapped memory. This *might* be the fix for #1377, but I don't think it is, since it should print "Good, unrepresentable C strings cause errors", before testing all the FFI conversions. Nevertheless, the attached patch is pretty crucial I think. The patch converts the assumption of 0 size for unknown foreign types in estimate-foreign-result-size to an error, much like the code in estimate-foreign-result-location-size already did. I don't know why they weren't the same, so beware that this patch may break things. And finally, this patch also converts the foreign type "(enum x)" into an "integer" scrutiny type. Before it would just use "number", but we know it must be an integer rather than, say, a ratnum, cplxnum or flonum, so let's use that knowledge. Cheers, Peter
From a7bd09a7b014547a9c85653adfc90efc4d1a0af1 Mon Sep 17 00:00:00 2001
From: Peter Bex <pe...@more-magic.net>
Date: Mon, 19 Jun 2017 15:01:14 +0200
Subject: [PATCH] Add foreign result size computation for enums and enum
locations
Also, error out instead of assuming 0 size when encountering an
unknown type, because that is too dangerous an assumption.
Finally, we improve the scrutiny type of "enum" to be "integer" rather
than the nondescript "number".
---
support.scm | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/support.scm b/support.scm
index 233ad961..a9d67ed9 100644
--- a/support.scm
+++ b/support.scm
@@ -1144,6 +1144,8 @@
;;; Compute foreign result size:
(define (estimate-foreign-result-size type)
+ (define (err t)
+ (quit-compiling "cannot compute size for unknown foreign type `~S' result" type))
(follow-without-loop
type
(lambda (t next)
@@ -1168,8 +1170,9 @@
(case (car t)
((ref nonnull-pointer pointer c-pointer nonnull-c-pointer function instance instance-ref nonnull-instance)
(words->bytes 3) )
- (else 0) ) )
- (else 0) ) ) ) )
+ ((enum) (words->bytes 6)) ; 1 bignum digit on 32-bit (overallocs on 64-bit)
+ (else (err t)) ) )
+ (else (err t)) ) ) ) )
(lambda () (quit-compiling "foreign type `~S' refers to itself" type)) ) )
(define (estimate-foreign-result-location-size type) ; Used only in compiler.scm
@@ -1179,8 +1182,8 @@
type
(lambda (t next)
(case t
- ((char int short bool unsigned-short unsigned-char unsigned-int long unsigned-long byte unsigned-byte
- c-pointer nonnull-c-pointer unsigned-integer integer float c-string symbol
+ ((char int short bool unsigned-short unsigned-char unsigned-int long unsigned-long byte
+ unsigned-byte c-pointer nonnull-c-pointer unsigned-integer integer float c-string symbol
scheme-pointer nonnull-scheme-pointer int32 unsigned-int32 integer32 unsigned-integer32
unsigned-c-string unsigned-c-string* nonnull-unsigned-c-string*
nonnull-c-string c-string* nonnull-c-string* c-string-list c-string-list*)
@@ -1193,7 +1196,7 @@
((pair? t)
(case (car t)
((ref nonnull-pointer pointer c-pointer nonnull-c-pointer function
- scheme-pointer nonnull-scheme-pointer)
+ scheme-pointer nonnull-scheme-pointer enum)
(words->bytes 1))
(else (err t)) ) )
(else (err t)) ) ) ) )
@@ -1293,7 +1296,7 @@
((ref pointer function c-pointer)
'(or boolean pointer locative))
((const) (foreign-type->scrutiny-type (cadr t) mode))
- ((enum) 'number)
+ ((enum) 'integer)
((nonnull-pointer nonnull-c-pointer) 'pointer)
(else '*)))
(else '*))))))
--
2.11.0
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