Makefile: Don't attempt to auto-detect stack size

We probe the available stack limit in the Makefile using rlimit, then use
that to set the size of the stack when we clone() extra threads.  But
the rlimit at compile time need not be the same as the rlimit at runtime,
so that's not particularly sensible.

Ideally, we'd set the stack size based on an estimate of the actual
maximum stack usage of all our clone()ed functions.  We don't have that
at the moment, but to keep things simple just set it to 1MiB - that's what
the current probe will set things to on my default configuration Fedora 40,
so it's likely to be fine in most cases.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Makefile

@@ -15,11 +15,6 @@ VERSION ?= $(shell git describe --tags HEAD 2>/dev/null || echo "unknown\ versio
 # the IPv6 socket API? (Linux does)
 DUAL_STACK_SOCKETS := 1
 
-RLIMIT_STACK_VAL := $(shell /bin/sh -c 'ulimit -s')
-ifeq ($(RLIMIT_STACK_VAL),unlimited)
-RLIMIT_STACK_VAL := 1024
-endif
-
 TARGET ?= $(shell $(CC) -dumpmachine)
 # Get 'uname -m'-like architecture description for target
 TARGET_ARCH := $(shell echo $(TARGET) | cut -f1 -d- | tr [A-Z] [a-z])
@@ -36,7 +31,6 @@ FLAGS := -Wall -Wextra -Wno-format-zero-length
 FLAGS += -pedantic -std=c11 -D_XOPEN_SOURCE=700 -D_GNU_SOURCE
 FLAGS +=  $(FORTIFY_FLAG) -O2 -pie -fPIE
 FLAGS += -DPAGE_SIZE=$(shell getconf PAGE_SIZE)
-FLAGS += -DRLIMIT_STACK_VAL=$(RLIMIT_STACK_VAL)
 FLAGS += -DVERSION=\"$(VERSION)\"
 FLAGS += -DDUAL_STACK_SOCKETS=$(DUAL_STACK_SOCKETS)
 

util.h

@@ -132,7 +132,7 @@ static inline uint32_t ntohl_unaligned(const void *p)
 	return ntohl(val);
 }
 
-#define NS_FN_STACK_SIZE	(RLIMIT_STACK_VAL * 1024 / 8)
+#define NS_FN_STACK_SIZE	(1024 * 1024) /* 1MiB */
 int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
 	     void *arg);
 #define NS_CALL(fn, arg)						\