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When are shared library functions loaded into the heap?
What and where are the stack and heap?Which is faster: Stack allocation or Heap allocationHow do function pointers in C work?How do I use extern to share variables between source files?Improve INSERT-per-second performance of SQLite?Difference between static and shared libraries?Issue with threads: value stored in heapInstruction Type and CountIs it possible to identify whether an address reference belongs to static/heap/stack in the process address spaceDeleting a heap variable giving munmap_chunk(): invalid pointer error
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(This question concerns only the logical addresses)
I was experimenting with some code where I print out the addresses of different types/scopes of variables to better visualize the process image.
My confusion arose when I printed the addresses a few variables that have been allocated on the heap by malloc, and then also printed the address of the printf function out of curiosity.
What I discovered is that printf was being stored at a much higher address (ie closer to the stack) on the heap than my malloc allocated variables. This doesn't make sense to me because I assumed that the library functions would be loaded on the heap first thing at runtime before any other instructions are executed. I even put a printf statement before any malloc statements, in case library functions were loaded on the fly as they were needed, but it didn't change anything.
Thanks.
c memory heap
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
add a comment |
(This question concerns only the logical addresses)
I was experimenting with some code where I print out the addresses of different types/scopes of variables to better visualize the process image.
My confusion arose when I printed the addresses a few variables that have been allocated on the heap by malloc, and then also printed the address of the printf function out of curiosity.
What I discovered is that printf was being stored at a much higher address (ie closer to the stack) on the heap than my malloc allocated variables. This doesn't make sense to me because I assumed that the library functions would be loaded on the heap first thing at runtime before any other instructions are executed. I even put a printf statement before any malloc statements, in case library functions were loaded on the fly as they were needed, but it didn't change anything.
Thanks.
c memory heap
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
2
With virtual memory management, there's no reason to have any expectations about the addresses of the stack, heap, and code. And in fact, Address space layout randomization (ASLR) is specifically designed to foil attempts at predicting address relationships.
– user3386109
Mar 28 at 2:05
add a comment |
(This question concerns only the logical addresses)
I was experimenting with some code where I print out the addresses of different types/scopes of variables to better visualize the process image.
My confusion arose when I printed the addresses a few variables that have been allocated on the heap by malloc, and then also printed the address of the printf function out of curiosity.
What I discovered is that printf was being stored at a much higher address (ie closer to the stack) on the heap than my malloc allocated variables. This doesn't make sense to me because I assumed that the library functions would be loaded on the heap first thing at runtime before any other instructions are executed. I even put a printf statement before any malloc statements, in case library functions were loaded on the fly as they were needed, but it didn't change anything.
Thanks.
c memory heap
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
(This question concerns only the logical addresses)
I was experimenting with some code where I print out the addresses of different types/scopes of variables to better visualize the process image.
My confusion arose when I printed the addresses a few variables that have been allocated on the heap by malloc, and then also printed the address of the printf function out of curiosity.
What I discovered is that printf was being stored at a much higher address (ie closer to the stack) on the heap than my malloc allocated variables. This doesn't make sense to me because I assumed that the library functions would be loaded on the heap first thing at runtime before any other instructions are executed. I even put a printf statement before any malloc statements, in case library functions were loaded on the fly as they were needed, but it didn't change anything.
Thanks.
c memory heap
c memory heap
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
asked Mar 28 at 1:51
Luke4211Luke4211
143 bronze badges
143 bronze badges
2
With virtual memory management, there's no reason to have any expectations about the addresses of the stack, heap, and code. And in fact, Address space layout randomization (ASLR) is specifically designed to foil attempts at predicting address relationships.
– user3386109
Mar 28 at 2:05
add a comment |
2
With virtual memory management, there's no reason to have any expectations about the addresses of the stack, heap, and code. And in fact, Address space layout randomization (ASLR) is specifically designed to foil attempts at predicting address relationships.
– user3386109
Mar 28 at 2:05
2
2
With virtual memory management, there's no reason to have any expectations about the addresses of the stack, heap, and code. And in fact, Address space layout randomization (ASLR) is specifically designed to foil attempts at predicting address relationships.
– user3386109
Mar 28 at 2:05
With virtual memory management, there's no reason to have any expectations about the addresses of the stack, heap, and code. And in fact, Address space layout randomization (ASLR) is specifically designed to foil attempts at predicting address relationships.
– user3386109
Mar 28 at 2:05
add a comment |
1 Answer
1
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(This answer concerns Unix only. I don't know how it is on Windows.)
Most shared libraries are loaded into RAM before control reaches main, and the library containing printf definitely will be. The functions in dlfcn.h can be used to load more shared libraries during execution of the program, that's the most important exception.
Shared libraries have never been loaded as part of the "heap", if by that you mean the region of memory used to satisfy malloc requests. They are loaded using the system primitive mmap, and could be placed anywhere at all in memory. As user3386109 pointed out in a comment on the question, on modern systems, their locations are intentionally randomized as a countermeasure for various exploits.
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
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(This answer concerns Unix only. I don't know how it is on Windows.)
Most shared libraries are loaded into RAM before control reaches main, and the library containing printf definitely will be. The functions in dlfcn.h can be used to load more shared libraries during execution of the program, that's the most important exception.
Shared libraries have never been loaded as part of the "heap", if by that you mean the region of memory used to satisfy malloc requests. They are loaded using the system primitive mmap, and could be placed anywhere at all in memory. As user3386109 pointed out in a comment on the question, on modern systems, their locations are intentionally randomized as a countermeasure for various exploits.
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
add a comment |
(This answer concerns Unix only. I don't know how it is on Windows.)
Most shared libraries are loaded into RAM before control reaches main, and the library containing printf definitely will be. The functions in dlfcn.h can be used to load more shared libraries during execution of the program, that's the most important exception.
Shared libraries have never been loaded as part of the "heap", if by that you mean the region of memory used to satisfy malloc requests. They are loaded using the system primitive mmap, and could be placed anywhere at all in memory. As user3386109 pointed out in a comment on the question, on modern systems, their locations are intentionally randomized as a countermeasure for various exploits.
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
add a comment |
(This answer concerns Unix only. I don't know how it is on Windows.)
Most shared libraries are loaded into RAM before control reaches main, and the library containing printf definitely will be. The functions in dlfcn.h can be used to load more shared libraries during execution of the program, that's the most important exception.
Shared libraries have never been loaded as part of the "heap", if by that you mean the region of memory used to satisfy malloc requests. They are loaded using the system primitive mmap, and could be placed anywhere at all in memory. As user3386109 pointed out in a comment on the question, on modern systems, their locations are intentionally randomized as a countermeasure for various exploits.
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
(This answer concerns Unix only. I don't know how it is on Windows.)
Most shared libraries are loaded into RAM before control reaches main, and the library containing printf definitely will be. The functions in dlfcn.h can be used to load more shared libraries during execution of the program, that's the most important exception.
Shared libraries have never been loaded as part of the "heap", if by that you mean the region of memory used to satisfy malloc requests. They are loaded using the system primitive mmap, and could be placed anywhere at all in memory. As user3386109 pointed out in a comment on the question, on modern systems, their locations are intentionally randomized as a countermeasure for various exploits.
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
answered Mar 28 at 2:13
zwolzwol
104k27 gold badges184 silver badges287 bronze badges
104k27 gold badges184 silver badges287 bronze badges
add a comment |
add a comment |
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With virtual memory management, there's no reason to have any expectations about the addresses of the stack, heap, and code. And in fact, Address space layout randomization (ASLR) is specifically designed to foil attempts at predicting address relationships.
– user3386109
Mar 28 at 2:05