[Minios-devel] [UNIKRAFT PATCH v2 5/5] lib/syscall_shim: Option to generate libc-style stubs

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Introduces the option to automatically generate libc-style system call
stubs for unavailable system calls. With this function, it is possible
to provide all libc-style system call symbols although just a subset
of the full API is implemented. The symbols are defined as `weak` and
can be replaced by non-weak symbol definitions.

Signed-off-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
---
 lib/syscall_shim/Config.uk          | 15 +++++++++++++++
 lib/syscall_shim/Makefile.uk        |  8 ++++++++
 lib/syscall_shim/gen_libc_stubs.awk | 16 ++++++++++++++++
 3 files changed, 39 insertions(+)
 create mode 100644 lib/syscall_shim/gen_libc_stubs.awk

diff --git a/lib/syscall_shim/Config.uk b/lib/syscall_shim/Config.uk
index c3369463..9c39ed2f 100644
--- a/lib/syscall_shim/Config.uk
+++ b/lib/syscall_shim/Config.uk
@@ -9,6 +9,21 @@ if LIBSYSCALL_SHIM
        bool
        default n
 
+       config LIBSYSCALL_SHIM_LIBCSTUBS
+       depends on !LIBSYSCALL_SHIM_NOWRAPPER
+       bool "Provide libc-style stubs"
+       default n
+       help
+               Automatically generate libc-style stubs for unavailable
+               system calls. The aim is to provide all libc-style system
+               call symbols although just a subset of the full API may be
+               implemtented. The symbols are defined as `weak`.
+               Please note that depending on the used compiler and optimization
+               options, this functionality may sometimes cause linking failures
+               because of double definitions of symbols. This is the case when
+               another library is providing some libc-style system calls
+               without registering them to libsyscall_shim.
+
        config LIBSYSCALL_SHIM_HANDLER
                bool "Binary system call handler (Linux ABI)"
                default n
diff --git a/lib/syscall_shim/Makefile.uk b/lib/syscall_shim/Makefile.uk
index c01ee494..d3bfe4f8 100644
--- a/lib/syscall_shim/Makefile.uk
+++ b/lib/syscall_shim/Makefile.uk
@@ -12,6 +12,7 @@ LIBSYSCALL_SHIM_GEN_SRC += 
$(LIBSYSCALL_SHIM_BUILD)/uk_syscall.c
 LIBSYSCALL_SHIM_GEN_SRC += $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_r.c
 LIBSYSCALL_SHIM_GEN_SRC += $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_name.c
 LIBSYSCALL_SHIM_GEN_SRC += $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_name_p.c
+LIBSYSCALL_SHIM_GEN_SRC += $(LIBSYSCALL_SHIM_BUILD)/libc_stubs.c
 
 UK_PREPARE-$(CONFIG_LIBSYSCALL_SHIM) += $(LIBSYSCALL_SHIM_PHONY_SRC) 
$(LIBSYSCALL_SHIM_GEN_SRC)
 
@@ -65,6 +66,11 @@ $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_name_p.c: 
$(LIBSYSCALL_SHIM_BUILD)/provided_
        $(call build_cmd,GEN,libsyscall_shim,$(notdir $@), \
                $(AWK) -F '-' -f 
$(LIBSYSCALL_SHIM_BASE)/gen_uk_syscall_name_p.awk $< > $@)
 
+$(LIBSYSCALL_SHIM_BUILD)/libc_stubs.c: 
$(LIBSYSCALL_SHIM_BASE)/gen_libc_stubs.awk $(LIBSYSCALL_SHIM_TEMPL)
+       $(call build_cmd,GEN,libsyscall_shim,$(notdir $@), \
+               $(AWK) -f $(LIBSYSCALL_SHIM_BASE)/gen_libc_stubs.awk \
+               $(LIBSYSCALL_SHIM_TEMPL) > $@)
+
 $(LIBSYSCALL_SHIM_BUILD)/provided_syscalls.h.in.new:
        $(call build_cmd,GEN,libsyscall_shim,$(notdir $@), \
                echo $(UK_PROVIDED_SYSCALLS-y) | tr ' ' '\n' > $@)
@@ -85,5 +91,7 @@ LIBSYSCALL_SHIM_SRCS-y += 
$(LIBSYSCALL_SHIM_BUILD)/uk_syscall.c
 LIBSYSCALL_SHIM_SRCS-y += $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_r.c
 LIBSYSCALL_SHIM_SRCS-y += $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_name.c
 LIBSYSCALL_SHIM_SRCS-y += $(LIBSYSCALL_SHIM_BUILD)/uk_syscall_name_p.c
+LIBSYSCALL_SHIM_SRCS-$(CONFIG_LIBSYSCALL_SHIM_LIBCSTUBS) += 
$(LIBSYSCALL_SHIM_BUILD)/libc_stubs.c
+LIBSYSCALL_SHIM_LIBC_STUBS_FLAGS+=-fno-builtin 
-Wno-builtin-declaration-mismatch
 
 LIBSYSCALL_SHIM_CLEAN = $(LIBSYSCALL_SHIM_PHONY_SRC) 
$(LIBSYSCALL_SHIM_PHONY_SRC_NEW) $(LIBSYSCALL_SHIM_GEN_SRC) 
$(LIBSYSCALL_SHIM_GEN_SRC)
diff --git a/lib/syscall_shim/gen_libc_stubs.awk 
b/lib/syscall_shim/gen_libc_stubs.awk
new file mode 100644
index 00000000..265c8fa9
--- /dev/null
+++ b/lib/syscall_shim/gen_libc_stubs.awk
@@ -0,0 +1,16 @@
+BEGIN {
+       print "/* Auto generated file. Do not edit */"
+       print "\n#include <errno.h>"
+       print "\n#include <uk/syscall.h>"
+       print "\n#include <uk/print.h>"
+       print "\n#include <uk/essentials.h>"
+}
+/#define __NR_/ {
+       name = substr($2,6);
+       printf "\n#ifndef HAVE_uk_syscall_%s", name;
+       printf "\nlong __weak %s(void)", name;
+       printf "\n{";
+       printf "\n\treturn uk_syscall_e_stub(\"%s\");", name;
+       printf "\n}";
+       printf "\n#endif /* !HAVE_uk_syscall_%s */\n", name;
+}
-- 
2.20.1


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